What is the waste factor in concrete calculations?

It covers the material lost to spillage, uneven ground and formwork that spreads, on top of the exact volume. The waste percentage is yours to set; the tool starts at 10%, and the concrete to order and the dry materials both include it.

How do I calculate concrete for a round post hole or column?

Volume = π × radius² × depth, the volume of a cylinder. For a 10-inch diameter hole (5-inch radius) that is 3 feet deep: π × 0.417² × 3 = 1.64 cubic feet. Select the Circular Column shape in this calculator and enter the diameter and height.

What concrete mix ratio is best for a slab?

The code where you build sets the minimum strength. In IS 456, reinforced concrete needs at least M20 even in mild exposure (Table 5), about a 1:1.5:3 mix, and nominal mixes stop at M20. Plain concrete may use lower grades. Select the mix that meets your grade, or switch to Custom Mix.

How much cement, sand and aggregate do I need for 1 cubic metre of M20 concrete?

M20 is about a 1:1.5:3 mix by volume. For 1 cubic meter of finished concrete the calculator starts from a dry volume of 1.54 cubic meters and splits it by that ratio: 403.2 kg of cement (rounded up to 9 bags of 50 kg, 17 of 25 kg or 10 US 94 lb sacks), 672 kg of sand (420 litres), 1.26 tonnes of aggregate (840 litres) and 181 litres of water at the 0.45 water-cement ratio the M20 mix fills in. Those figures carry no waste. The waste factor is added on top, so at 10% the cement becomes 443.5 kg and the water 200 litres. The weights use bulk densities of cement 1,440 kg, sand 1,600 kg and aggregate 1,500 kg per cubic meter, so treat them as an ordering estimate. The first two are IS 875's; the third is CalcTrail's own. For M15 (1:2:4) the same cubic meter takes 316.8 kg of cement, 704 kg of sand and 1.32 tonnes of aggregate.

What units can I get the results in?

Volumes are shown in cubic meters (litres for small pours), with the concrete to order also in cubic yards. Materials come in kilograms or tonnes, and water in litres and US gallons. The inputs accept meters, centimeters, feet and inches, so the calculator works in metric or US units alike, and you can enter a 10-inch hole and a 3-foot depth directly. To check by hand, multiply length × width × thickness in feet and divide by 27 for cubic yards, before waste.

Concrete Calculator - Bags, Cubic Yards & Mix Quantities

Parameters

Concrete to order in cubic yards or meters, 40, 60 and 80 lb bag counts, and the cement, sand, aggregate and water for M5 to M20, two richer mixes or your own.

Choose a shape

Pick a mix

Set wastage percentage

Review material requirements

This sizes the pour from the dimensions and mix ratio you entered, applies the waste percentage you set, and uses a fixed 1.54 dry-to-wet factor, a site rule of thumb, for the cement, sand and stone quantities. Bag counts are rounded up. Confirm the final quantity with your supplier before ordering.

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.

Wet volume, box shapes

Standard Mix and Custom Mix modes, for a slab, rectangular column or footing

Wet Volume = Length × Width × Height, in metres

Wet Volume: the space the pour fills

Source: Standard formula; no single publisher.

Wet volume, circular column

Standard Mix and Custom Mix modes, for a circular column

Wet Volume = π × (Diameter / 2)² × Height, in metres

Wet Volume: the space the pour fills

Source: Standard formula; no single publisher.

Wet volume, entered

Standard Mix and Custom Mix modes, for a custom volume

Wet Volume = Entered volume

Source: The volume you type; no publisher.

Dry volume and concrete to order

Standard Mix and Custom Mix modes

Dry Volume = Wet Volume × 1.54 Dry Material = Dry Volume × (1 + Waste%) To Order = Wet Volume × (1 + Waste%)

Wet Volume: the space the pour fills
Dry Volume: loose cement, sand and aggregate before mixing
Dry Material: the dry volume with waste
To Order: ready-mix or bagged concrete, with waste

The 1.54 applies to the loose dry ingredients only; concrete is bought by the To Order volume.

Source: The 1.54 factor is widely used; no primary source found (IS 456 and IS 875 searched). The 10% starting waste is CalcTrail's own; no publisher.

Cement, sand, aggregate and water

Standard Mix and Custom Mix modes

Part's mass = (its parts ÷ all parts) × Dry Material × bulk density Water = cement mass × water-cement ratio

Dry Material: the dry volume with waste

1:5:10 to 1:1.5:3: about the IS 456 nominal mixes M5, M7.5, M10, M15 and M20
1:1:2, 1:0.75:1.5: rich mixes with no IS 456 nominal grade

Bulk densities: cement 1,440, sand 1,600 and aggregate 1,500 kg/m³. In IS 456 the number after M is the strength of a 150 mm cube at 28 days, in N/mm², and nominal mixes stop at M20; a design mix is preferred.

Source: Based on IS 456:2000, clause 9.3 and Table 9, by mass there and by volume here (within 4.2%) [1]; cement and sand densities from IS 875 (Part 1), Table 1 [2]. The aggregate's 1,500, between IS 875's shingle (1,460) and ballast (1,600 to 1,870), the water-cement ratios and the two rich mixes are CalcTrail's own; no publisher.

Bags

Standard Mix and Custom Mix modes

Premixed bags = To Order (ft³) ÷ yield per bag, rounded up

To Order: the concrete to order

Yields: 40 lb 0.30 ft³, 60 lb 0.45 ft³, 80 lb 0.60 ft³. Cement sacks are the cement mass over 50 kg, 25 kg or 94 lb, rounded up.

Source: Uses the bag yields Quikrete publishes for its Concrete Mix No. 1101 [3]; other brands may differ.

Sources

Bureau of Indian Standards (BIS). IS 456:2000, Plain and Reinforced Concrete, Code of Practice, clauses 5.6.3, 6.2.3.1 and 9.3; Tables 2, 5 and 9. Fourth revision, July 2000.
Bureau of Indian Standards (BIS). IS 875 (Part 1):1987, Unit Weights of Building Materials and Stored Materials, Table 1. 1987.
The Quikrete Companies. QUIKRETE Concrete Mix, Product No. 1101, product data sheet, Yield. Revised October 2022.

What this calculator does not cover

This turns dimensions into volumes and a mix ratio into material quantities. It does not design a mix for a strength, or allow for moisture in the sand, admixtures, air entrainment or the volume of reinforcement.
It does not tell you which grade your work needs: that is set by the code where you build.

Sources checked on October 5, 2026.

Help

Choose a shape: Pick a predefined shape (slab, column, footing) and enter dimensions, or pick Custom Volume to enter a known volume directly.
Pick a mix: Select a standard mix (M5 to M20, or a rich mix) or switch to Custom Mix to set your own cement:sand:aggregate ratio.
Set wastage percentage: Account for spillage, cuts and shrinkage. The tool starts at 10%.
Review material requirements: See cement, sand, aggregate, and water quantities needed.
View results: Get total volume, material weights, and number of cement bags.

Understanding Concrete Volume & Mix Design

Bags to buy, or materials to batch

A concrete job comes with one of two shopping lists. Buying pre-mixed bags or ready-mix, you need the volume and a bag count. Mixing on site, you need the cement, sand, aggregate and water for a given mix. This calculator gives both from the same dimensions: the "Concrete to Order" in cubic meters and cubic yards with its 40, 60 and 80 lb bag counts, and the materials for a mix from M5 to M20, two richer mixes or a ratio you enter, with the cement also counted in 50 kg, 25 kg and 94 lb sacks.

Why dry volume is larger than wet volume

The wet volume is the space the finished pour will fill. Dry cement, sand and aggregate take up more room before mixing with water, because of the air gaps between particles. So the calculator multiplies the wet volume by 1.54, a site rule for loose ingredients with no single published source. Ordering ready-mix instead? The amount of concrete to order is the "Concrete to Order" figure at the top: the wet volume plus your waste allowance.

Reading a mix ratio like 1:2:4

A mix ratio states cement : sand : aggregate by volume. 1:2:4 means 1 part cement to 2 parts sand and 4 parts aggregate. That is about the M15 nominal mix of IS 456 Table 9: 15 N/mm² on a 150 mm cube at 28 days. Richer mixes (more cement relative to aggregate) give stronger concrete. The code where you build sets the grade a job needs.

Water-cement ratio

The water-cement ratio controls both workability and final strength. Too little water makes concrete hard to place and compact; too much water weakens the cured concrete. Picking a standard mix fills in CalcTrail's ratio for it (0.60 down to 0.40), within the IS 456 limits for M5 to M20. You can edit it, and the water quantity follows what you enter.

Why add a waste factor

Spillage, over-excavation, formwork that spreads and material lost in mixing and placing all mean you need more than the theoretical volume. The waste percentage is yours to set; the tool starts at 10%.

Cement sacks, and pre-mixed bags

Cement is reported as a weight in kilograms and as a sack count in all three common sizes: 50 kg, 25 kg and the US 94 lb sack. Separately, the pre-mixed bag count says how many 40, 60 or 80 lb bags of ready-to-use concrete the pour takes. It comes from the concrete to order, not from the cement weight. In the US, portland cement is sold in 94 lb sacks, so the cement is counted in those as well as in 50 kg and 25 kg bags.

Frequently Asked Questions

Two different bags, and the calculator gives both. Buying ready-to-use concrete: the 40, 60 and 80 lb bag counts come from the volume you are pouring, at Quikrete's published yields of 0.30, 0.45 and 0.60 cubic feet a bag: 90, 60 and 45 bags to the cubic yard. Batching your own mix: the cement bag counts come from the cement weight instead, in 50 kg, 25 kg and US 94 lb sacks. Counts are rounded up and your waste factor is already in the volume they come from.

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Last updated October 12, 2026

Concrete Calculator - Bags, Cubic Yards & Mix Quantities

Formulas and sources

Wet volume, box shapes

Wet volume, circular column

Wet volume, entered

Dry volume and concrete to order

Cement, sand, aggregate and water

Bags

Sources

What this calculator does not cover

Help

Quick Start Guide

Understanding Concrete Volume & Mix Design

Bags to buy, or materials to batch

Why dry volume is larger than wet volume

Reading a mix ratio like 1:2:4

Water-cement ratio

Why add a waste factor

Cement sacks, and pre-mixed bags

Features

Common Use Cases

Frequently Asked Questions

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