What is the unit price formula?

Unit price, also called unit cost or the unit selling price of a pack, = total price ÷ quantity. For example, a 500 g pack at $3.00 has a unit price of $0.006 per gram. The calculator applies this to every item and normalizes the units, so you can compare grams vs kilograms, ounces vs pounds, and so on.

How do I work out the price per item or per piece?

Measure by Count (per item): choose what you are comparing, then Count under Measured by, and enter how many items each pack holds (24 for a 24-pack) with the unit set to Item or Piece (a Dozen counts as 12). The calculator divides each price by its count and ranks the packs by cost per item. A 24-pack at $8.99 comes to about $0.375 an item and a 60-pack at $19.99 to about $0.333, so the bigger pack is cheaper for each item even though it costs more to buy.

How do I compare a multi-buy, like 4 for $5 or buy one get one free?

Set Priced as on the item. For 4 for $5, choose N for a price and enter 4, $5 and the size of one. For buy one, get one free, choose Buy X, get Y free and enter the price of one, buy 1 and get 1 free: the deal is priced as two for the price of one. A percent off when you buy several works the same way. Where a store sells a single item at the multi-buy rate, enter it as a price each. Every item that is not the best also shows the price it would need to match the best.

Can I compare items sold in different sizes or units?

Yes. Choose what you are comparing and how it is measured: weight, volume, length, area, count (per item), data, energy or time. Then pick the unit for each item within it, such as grams vs kilograms, ounces vs pounds, US vs UK pints, or square feet vs square yards. The calculator converts everything to a common unit before ranking, so the comparison is fair even when the sizes or units do not match.

Can I compare subscription, rental, or hourly rates?

Yes. Choose Time and subscriptions to compare anything priced per minute, hour, day, week, month, or year: a monthly vs. annual subscription, an hourly freelance or labor rate, or a daily vs. weekly rental. The calculator converts every price to the same time unit (e.g. dollars per month) before ranking, the same way it does for groceries. A month is the average month of 30.4375 days and a year is 365.25 days. Enter how long you need it to count an intro price or a one-time fee.

Is a yearly plan worth it if I might cancel?

Enter how long you need it, and the calculator prices each plan for that long in whole payments, with any intro price and one-time fee. A $10.99 monthly plan whose first 3 months cost $0.99 comes to $57.92 for 8 months, against $99 for a year paid up front. Kept 12 months, the monthly plan costs $101.88, and the yearly plan wins by $2.88. The cheapest way can also mix plans, such as a year and then a few months.

How do I compare phone plans with an activation fee?

Choose Time and subscriptions, enter each plan’s monthly price, and add its one-time fee. Once you enter how long you need it, the fee counts once. Over 24 months a $35 plan with a $35 activation fee costs $875, against $960 for a $40 plan with none. Over 6 months the $40 plan is cheaper, $240 against $245, and from 8 months the plan with the fee wins. A contract that ties you in for 24 months is one purchase: enter its price for the 24 months.

What does Discount & Tax mode do?

Simple mode compares the plain price per unit. Discount & Tax mode applies a coupon or sale to each item before ranking, and adds sales tax when Include tax is ticked, which can flip the winner. In the same mode an item can take a usable yield, so you compare the price of what you actually use, as with fresh food that gets trimmed, and a store membership. In any mode you can also rank by cost per use, such as per serving or per load, where what you compare is used up a use at a time.

How do I find the cheapest way to buy a set amount?

Enter how much you need, such as 80 L of paint. The calculator works out the cheapest way to buy at least that much from the items listed, in whole packs, and says what is left over. For 80 L, 23 tins of 3.5 L at $12.60 cost $289.80 with 0.5 L left over, while four 20 L buckets at $75 cost $300. It lists each item bought alone too, and a mix of sizes when one is cheaper.

How do I compare paint by what it covers?

Choose Building and DIY, measure by volume, and rank by cost per sq ft. Enter what each pack covers in one coat, from its label. A 1-gallon can at $38 that covers 400 sq ft costs $0.095 a sq ft, and a 5-gallon bucket at $165 that covers 2,000 sq ft costs $0.0825. Then enter the area and the coats: for 1,100 sq ft and 2 coats, the cheapest way is one 5-gallon bucket and one gallon, $203. For flooring and tiles, add a waste allowance for cuts.

How do I compare electricity or gas plans with a fixed charge?

Choose Electricity and gas, then enter each plan’s unit rate, its fixed charge (a standing, base or daily supply charge) a day or a month, and how much you use. Type rates in your currency, such as 0.145 for 14.5¢; the field shows the cents under it. Each plan is ranked by its all-in price per kWh at your usage. A plan at 14.5¢ a kWh with $9.95 a month costs $154.95 at 1,000 kWh a month, against $148.95 for one at 12.9¢ with $19.95 a month. Below 625 kWh a month the first is cheaper. For an off-peak plan, add its off-peak rate and the share of your use at those times.

Does a warehouse club membership change which is cheaper?

It can. In Discount & Tax mode, add a membership to an item: its yearly fee and what you spend at that store in a month. The fee is spread over that spending, so a $65 fee over $40 a month adds 13.5% to the store’s prices, which can turn a cheap-looking bulk pack into the dearer one. The more you spend there, the less of the fee each item carries: at $400 a month the same fee adds 1.4%.

How do I compare cost per load, per sheet or per serving?

Choose what you are comparing, rank by cost per use, and enter the uses in each pack. They are the loads or washes on a detergent, the sheets in a pack of paper towels (rolls × sheets per roll), the servings on a food label, the doses in a bottle of supplements, or the days a pack lasts you. Each price is divided by its uses. A 64-load detergent at $11.99 is about $0.19 a load and a 96-load one at $16.99 about $0.18, so the bigger bottle wins per load. Cost per use is not a unit price in NIST’s sense.

How are the savings projections calculated?

With at least two items priced, the saving per purchase is what one purchase of the best option saves against buying the same amount at the next-best price. For example, 24 oz for $7.99 against 12 oz for $4.49 saves $0.99. In Discount & Tax mode, that saving is multiplied by your monthly purchases for the monthly and yearly figures. The field starts at 4, and the card says the count it used.

Price Comparison Calculator - Cheapest Price per Unit

Items to Compare

Compare price per item, piece, gram, ounce, or liter, or per hour, month, or year for subscriptions and rentals. See which is the better buy and what you save.

Add your first item

Add more items

Choose what you are comparing and the unit

Say how each price is stated (optional)

Prices, tax rates and yields are what you entered. Tax on a coupon depends on who pays for it and where you buy.

Formulas and sources

Each formula this calculator uses, where it comes from, and what it leaves out. "How it works" shows the same formula with your own numbers.

Unit price

Simple and Discount & Tax modes

Unit Price = Price ÷ Quantity

Unit Price: the price of one comparison unit
Price: the shelf price in Simple; the price after discount, tax and any membership in Discount & Tax
Quantity: the amount in the comparison unit

Two unit prices within one part in a billion count as a tie, and the first-listed item stays first.

Source: Standard formula; no single publisher. NIST defines unit pricing as the cost per unit of measure [1] and asks a store to unit price one commodity consistently [2].

Quantity in the comparison unit

Simple and Discount & Tax modes

Quantity = size × packs, in the comparison unit

Each unit converts by the Unit Converter’s exact factor, so 1 US gallon is exactly 128 US fluid ounces and 1 lb is 16 oz. A blank pack count, or one below 1, counts as 1. A multipack is priced as its total contents, as a multiunit package states them: 6 bars of 100 g is 600 g. N for a price counts N as the packs; a price each counts one; a shelf unit price counts the amount on its tag, and a blank amount is one of its unit.

Source: Uses the conversion method of NIST SP 811, Appendix B [3]. Pack totals are consistent with NIST Handbook 130, Section 10.4 [4].

Usable quantity

Discount & Tax mode, when an item has a usable yield, ranked by price per unit

Quantity = size × packs × usable yield, in the comparison unit

Yield is the share of the pack you can use after trimming or waste; blank or 100 means none is lost, and 0 or over 100 is refused. An apple that is 10% inedible has a 90% yield. Weight gained in cooking is not modeled.

Source: Based on the preparation-yield adjustment in USDA Economic Research Service’s fruit and vegetable price method [5].

Price and quantity of a deal

Simple and Discount & Tax modes, when an item is priced as a deal

Buy X, get Y free: Price = X × price each, Quantity = (X + Y) × size % off when you buy N: Price = N × price each × (1 − Percent ÷ 100), Quantity = N × size

A deal is priced as the purchase it asks for: buy 2, get 1 free at $3.49 is $6.98 for three. Blank counts read as buy 1, none free and 0% off. A coupon and tax, in Discount & Tax, then apply to that purchase.

Source: CalcTrail’s own; no publisher.

Price after discount and tax

Discount & Tax mode

Price = shelf price − discount + tax

A percent discount takes Price × Percent ÷ 100 off; an amount off larger than the price is refused, and that item is not ranked. Tax is then added to the discounted price: Price × (1 + Rate ÷ 100), at the item’s own rate or the default.

Source: Standard percentage formulas; no single publisher. NIST asks that a sale or coupon price carry its own unit price [1]. Adding tax after the discount is CalcTrail’s own assumption; the default rate of 8.25% is only a starting value.

Cost per use

Simple and Discount & Tax modes, when ranked by cost per use

Cost per Use = Price ÷ Uses

Cost per Use: what one use costs
Price: the price after any discount, tax and membership
Uses: what the whole pack gives, as the category counts it: servings, uses, sheets, days, doses, or the area paint covers

Uses are the number you enter in each item, named by what you compare: servings, uses (loads or washes), sheets, days, doses, or for paint and finishes sold by volume, the area a pack covers in one coat (sq ft or m²). Servings on a food label are rounded (to the nearest half from 2 to 5 servings). Yield does not enter it. NIST does not accept a serving as a unit of measure for unit prices, so this ranking sits beside the price per unit.

Source: CalcTrail’s own; no publisher. Servings on a label: 21 CFR 101.9 [6]; servings and unit prices: NIST SP 1181, Section 3 [1].

Price with a membership

Discount & Tax mode, when an item has a membership

Price = Price × (1 + Fee ÷ (12 × Monthly spend))

A store’s yearly membership fee is spread over what you spend there in a year, and the result is applied to the price after the discount and tax: a $65 fee over $40 a month adds 13.5% to its prices. An item with a fee and no monthly spend is not ranked until the spend is entered.

Source: CalcTrail’s own; no publisher.

The cheapest way to buy an amount

Simple and Discount & Tax modes, when you enter how much you need

Cost = Σ packs × price per pack, with Σ packs × size ≥ the amount you need

Packs are whole, so the amount is rounded up and what is left over is shown. Every mix of the listed items is searched, cheapest per unit first, and each item alone is listed too. On a very long list the search may stop at its limit, and then the panel says the mix is the cheapest found. Ranked per use, the amount and the sizes are in uses.

Source: CalcTrail’s own; no publisher.

An energy plan at your usage

Simple and Discount & Tax modes, in Electricity and gas, when you enter how much you use

Cost a month = rate × usage a month + fixed charge a month

A fixed charge a day counts 30.4375 days a month, and a year is 12 months. The plans rank by the all-in price per unit: the cost over the usage. Two plans cost the same at (fixed charge B − fixed charge A) ÷ (rate A − rate B) a month; the one with the lower fixed charge is cheaper below that usage. In Discount & Tax the fixed charge takes the same discount and tax as the rate. Without a usage the plans rank by their rates alone.

Source: CalcTrail’s own; no publisher.

Off-peak share

Simple and Discount & Tax modes, when a plan has an off-peak rate

Rate = peak rate × (1 − share) + off-peak rate × share

The share is the part of your use at the plan’s off-peak times, such as overnight charging, from 0% to 100%. Blank counts as 0%, so the off-peak rate does not count until a share is entered. One share is used for every plan.

Source: CalcTrail’s own; no publisher.

Area with coats and waste

Simple and Discount & Tax modes, in Building and DIY, when you enter the amount with coats or waste

Area = area × coats × (1 + waste ÷ 100)

The amount bought for, before the cheapest way to buy it is found. Coats count when paint or a finish is ranked by what a pack covers; waste is an allowance for cuts, breakage and offcuts, in any Building and DIY comparison. Blank coats count as 1 and blank waste as none.

Source: CalcTrail’s own; no publisher.

Intro prices and one-time fees

Simple and Discount & Tax modes, when a comparison in time has an intro price or a one-time fee, and you enter how long you need it

Cost = fee + intro price × intro payments + price × the other payments

For each item, over the payments that cover how long you need it: the one-time fee once, the intro price for its first payments (blank counts 1), then the regular price. The cheapest way may start on one plan’s intro price and move to another. The price per unit stays the regular price, and in Discount & Tax the intro price takes the same share of discount, tax and membership as the regular one.

Source: CalcTrail’s own; no publisher.

Price to match

Simple and Discount & Tax modes, when ranked by price per unit

Price to match = best unit price × quantity, before any tax, discount and deal

For each item that is not the best: the price its Price field would need, in the way it is stated (a pack, each, or per its tag’s amount), to tie the best. The membership, tax, the discount and the deal are taken back off in the reverse of the order they are applied, and the price is rounded down (to the cent, or below $1 to the digits a unit price shows) so it never loses. In Electricity and gas it is the unit rate that gives the same cost a month as the best plan at your usage, with the plan’s own fixed charge kept.

Source: CalcTrail’s own; no publisher.

Price to match, per use

Simple and Discount & Tax modes, when ranked by cost per use

Price to match = best cost per use × uses, before any tax and discount

A membership, tax, the discount and a deal are taken back off the same way, and the price is rounded down.

Source: CalcTrail’s own; no publisher.

Saving per purchase, per month and per year

Simple and Discount & Tax modes

Saving per purchase = (next best − best) × the amount in one purchase of the best.

It compares the best item with the second-best only, on one purchase of the best. In Discount & Tax, Per month is the saving per purchase × Monthly Purchases, and Per year is Per month × 12. Monthly Purchases starts at 4, and the card says the count it used. There is no Per month or Per year for plans measured in time, where each payment is already a period. In Electricity and gas the saving is shown a month and a year at your usage instead.

Source: CalcTrail’s own; no publisher.

How a unit price is shown

Every mode

From $1 up a unit price shows the currency’s two decimals; below $1 it shows three significant digits, such as $0.00382, so close prices stay apart. NIST Handbook 130’s model regulation has store labels round to the cent or the tenth of a cent; this calculator does not. For weight and volume the best value is also shown in the units shelf tags use: per ounce and pound and per 100 g and kg, or per fluid ounce and gallon and per 100 ml and liter. US dollars list the US units first; other currencies list the metric ones first.

Source: CalcTrail’s own display rule; no publisher. Store labels: [2].

Sources

National Institute of Standards and Technology. Unit Pricing Guide: A Best Practice Approach to Unit Pricing, Definitions, and Section 3. Special Publication 1181, June 2025.
National Institute of Standards and Technology. Handbook 130, Uniform Laws and Regulations in the Areas of Legal Metrology and Fuel Quality, Section IV.C, Uniform Unit Pricing Regulation, Sections 2, 4 and 6. 2026 edition.
National Institute of Standards and Technology. NIST Guide to the SI, Appendix B: Conversion Factors, B.2, B.3, B.5 and B.7.2, and footnotes 9, 18 and 24. Special Publication 811 (2008), web page updated August 18, 2025.
National Institute of Standards and Technology. Handbook 130, Uniform Laws and Regulations in the Areas of Legal Metrology and Fuel Quality, Section IV.A, Uniform Packaging and Labeling Regulation, Sections 2.8 and 10.4. 2026 edition.
US Department of Agriculture, Economic Research Service. Fruit and Vegetable Prices: Documentation, section "Estimating the Costs to Consume Fruits and Vegetables". Page updated December 9, 2025.
US Food and Drug Administration. Code of Federal Regulations, Title 21, §101.9: Nutrition labeling of food, §101.9(d)(3)(i), servings per container, and §101.9(b)(8), how the number is rounded. eCFR, current as of October 1, 2026.

What this calculator does not cover

It compares price per amount, not quality, nutrition, brand, expiry, storage or how much you will use.
It does not look up prices or tax rates. It prices the deals in its Priced as list as the purchase each asks for; a deal that needs a store card, a coupon book or a minimum spend is not modeled.
Weight cannot be compared with volume: converting needs the density of the product.
For electricity and gas it takes a unit rate, a fixed charge and one off-peak rate a plan. Tiered or slab rates, bill credits, demand charges, more than two time bands, solar export payments and gas in cubic metres are not modeled, and it knows no supplier’s prices.
Data, energy and time units use the same exact factors, but NIST’s retail unit-pricing rules cover only weight, volume, count, area and length.
A subscription is priced as whole payments of one regular price after any intro price. Price rises, minimum terms and cancellation fees are not modeled; enter a contract as one purchase for its term.
A store membership is spread over the spending you enter at that store. It does not say whether joining is worth it, and one fee is not shared across several items.
Paint coverage is the figure you enter from the label for one coat; the calculator does not estimate it.

Sources checked on October 6, 2026.

Help

Add your first item: Name it, then enter its price and quantity (e.g., $5.00 for 10 oz).
Add more items: Click "Add Item" for every other price or package size you want to compare.
Choose what you are comparing and the unit: Choose what you are comparing, such as groceries, paper goods or fuel, then how it is measured where there is a choice, and the unit to compare per. The calculator converts every item to that unit.
Say how each price is stated (optional): Under Priced as, choose N for a price, Price each, Shelf unit price, Buy X, get Y free or % off when you buy N, so you can type the price as the tag reads. Pack or bundle is the default.
Rank by cost per use (optional): Where a pack is used up a use at a time, set Rank By to cost per serving, load, sheet, day, dose or sq ft, and enter the uses in each pack.
Enter how much you need (optional): Type the amount, or how long you need a plan for, to see the cheapest way to buy at least that much in whole packs or payments, and what is left over.
View the verdict: See which item costs less per unit, how much more each other item costs per unit, and what one purchase of the best saves.
Adjust for discounts, tax, or waste (optional): Switch to Discount & Tax mode when a coupon, sales tax, a store membership or waste should factor into the comparison.
Export your results: Copy the comparison, or download it as JSON, CSV or PDF.

Understanding Price Comparison

What is unit price?

Unit price is what one standard amount costs: per gram, per ounce, per liter, per item. NIST calls unit pricing the cost per unit of measure. You get it by dividing the package price by its size: a $4.99 pack of 500 g works out to about $0.01 per gram. Comparing unit prices, rather than sticker prices, shows which option costs less per unit.

How to tell which is cheaper

Look at the price per unit, not the total price. A bigger box costs more overall. Enter each product’s price and size and the calculator ranks them, then highlights the lowest unit price as the best value. The price difference shows as the percent each other item costs more per unit than the best, and as the saving per purchase in dollars when two or more items are priced.

Is the bigger size always the better deal?

No. A larger pack can cost less per unit, and it can cost more. Some stores price the bigger size at a higher cost per unit, so the smaller pack wins. Compare the unit prices to know.

Comparing different sizes and units

Products rarely come in matching sizes: one is in grams, another in kilograms; one in fluid ounces, another in liters. Pick the unit for each item and the calculator converts everything to a common unit first, giving a normalized cost comparison that is fair. It also handles length, area, quantity, data (per GB, in the decimal units drives and data plans are sold in, so 1 TB is 1,000 GB), energy (per kWh) and time. Weight and volume cannot be compared directly, because converting needs the density of the product.

When the tag states the price another way

Not every tag reads as a price for a pack. Choose how each price is stated under Priced as: N for a price (4 for $5), a price each, the tag’s own unit price (per L, per kg or per 100 g), buy X get Y free, or a percent off when you buy several. Each becomes the price and the amount of one purchase, and they are compared the same way. Under the best value the price also shows in the units shelf tags use, per ounce and per pound or per 100 g and per kg, and every other item shows the price it would need to match the best.

When discounts, tax, and waste change the answer

Switch to Discount & Tax mode to apply a coupon or sale to each item before ranking, and tick Include tax to add sales tax; a discount can flip which option is cheapest. If part of a package is wasted (trimmed, spoiled, unusable), choose Add usable yield on that item and enter the share you can use, to compare the price of what you actually use.

Cost per load, per sheet or per serving

What a pack gives you is not always its size. Choose what you are comparing, and where a pack is used up a use at a time, rank by cost per use in any mode. It is named for what you compare: per serving for food and drinks, per use for detergents and cleaners, per sheet for paper goods, per day for baby and pet supplies, and per dose for supplements. A 64-load detergent at $11.99 costs about $0.19 a load, and a 96-load one at $16.99 about $0.18.

How much do you need?

Enter how much you need and the calculator finds the cheapest way to buy at least that much from the items listed. Packs are whole, so it rounds the amount up and says what is left over. For 80 L of paint, 23 tins of 3.5 L at $12.60 cost $289.80, against $300 for four 20 L buckets.

Subscriptions, intro prices and one-time fees

In a comparison measured in time, an item can take an intro price for its first payments and a one-time fee. Enter how long you need it, and each plan is priced for that long in whole payments. A $10.99 monthly plan with 3 months at $0.99 costs $57.92 for 8 months, against $99 for a year.

Store memberships

A club or store membership adds to the price of what you buy there. In Discount & Tax mode, add the yearly fee and what you spend at the store in a month. The fee is spread over that spending: $65 over $40 a month adds 13.5%, and over $400 a month 1.4%.

Paint, flooring and other building materials

Paint is bought by the can but used by the area it covers, so rank by cost per square foot from the coverage on the label. Enter the area and the coats, and the calculator finds the cheapest cans to buy. For flooring and tiles, add a waste allowance for cuts.

Electricity and gas plans

An energy plan has a price for each kWh and often a fixed daily or monthly charge. A lower rate with a higher fixed charge wins only above a certain usage. Enter your usage, and the plans are ranked by their all-in price per kWh, with the usage where the best two cost the same.

Mistakes to watch for

Judging by the sticker price instead of the price per unit; comparing mismatched units (grams against ounces) without converting; and ignoring waste on fresh food, where a cheaper package can cost more per usable portion. A single common unit removes the mismatch, and a usable yield in Discount & Tax mode covers waste.

Frequently Asked Questions

To compare prices fairly, compare the price per unit, not the total price. Enter two items or more, each with its price and size, and the calculator works out the cost per unit for each, then highlights the lowest one as the best value. A cheaper sticker price can lose once you account for how much you get.

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Last updated October 12, 2026

Price Comparison Calculator - Cheapest Price per Unit

Formulas and sources

Unit price

Quantity in the comparison unit

Usable quantity

Price and quantity of a deal

Price after discount and tax

Cost per use

Price with a membership

The cheapest way to buy an amount

An energy plan at your usage

Off-peak share

Area with coats and waste

Intro prices and one-time fees

Price to match

Price to match, per use

Saving per purchase, per month and per year

How a unit price is shown

Sources

What this calculator does not cover

Help

Quick Start Guide

Understanding Price Comparison

What is unit price?

How to tell which is cheaper

Is the bigger size always the better deal?

Comparing different sizes and units

When the tag states the price another way

When discounts, tax, and waste change the answer

Cost per load, per sheet or per serving

How much do you need?

Subscriptions, intro prices and one-time fees

Store memberships

Paint, flooring and other building materials

Electricity and gas plans

Mistakes to watch for

Features

Common Use Cases

Frequently Asked Questions

Related Calculators

Unit Converter

Percentage Calculator

Discount Calculator

Loan Calculator

Car Loan Calculator

Break-Even Calculator

Markup/Margin Calculator

Mortgage Calculator

Savings Calculator

Investment Calculator

Sales Tax Calculator

VAT Calculator