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.
Fuel and cost, US units
In US units
- Gallons
- the fuel needed, in US gallons
- Distance
- the trip distance, in miles
- MPG
- miles per US gallon
- Cost
- the fuel cost of the trip
- Price
- the price of one US gallon
The mileage is the one figure you enter.
Source: Standard formula; no single publisher. Units as NIST defines them [1]; what moves real mileage: fueleconomy.gov [2]; why ratings may not predict it [3].
Fuel and cost, metric units
In metric units
- Liters
- the fuel needed
- Distance
- the trip distance, in kilometers
- L/100km
- liters used per 100 kilometers
- Cost
- the fuel cost of the trip
- Price
- the price of one liter
Source: Standard formula; no single publisher.
Trip cost with extras
With Trip Extras
- Distance
- the distance you entered
- Round trip multiplier
- 2 for a round trip, 1 for one way
Tolls, parking and other costs are added once per trip, in your currency.
Source: Standard formula; no single publisher.
Per person and per month
- Passengers
- the people sharing the cost
- Trips per month
- from Trip Extras
Source: Standard formula; no single publisher.
Compare Vehicle
With Compare Vehicle
- Savings
- above zero, the other vehicle is cheaper
The other vehicle runs the same distance and extras through its own efficiency and price. Below zero, it costs more.
Source: Standard formula; no single publisher.
Switching units
- L/100km
- liters per 100 kilometers
- MPG
- miles per US gallon, not the imperial (UK) gallon
A switch converts with 1 mile = 1.609344 km and 1 US gallon = 3.785412 liters. It then rounds the economy to one decimal and the price to three, as a dashboard and a pump show them.
Source: Uses NIST's conversion factors [1].
Sources
- National Institute of Standards and Technology. NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, mile per gallon (U.S.), mile and gallon (U.S.). Special Publication 811, 2008 edition.
- U.S. Department of Energy and U.S. Environmental Protection Agency, fueleconomy.gov. Factors That Affect Fuel Economy. Undated page, read October 5, 2026.
- U.S. Department of Energy and U.S. Environmental Protection Agency, fueleconomy.gov. Your Mileage Will Vary. Undated page, read October 5, 2026.
What this calculator does not cover
- It estimates fuel cost only: no maintenance, insurance, depreciation or financing. The Car Loan Calculator covers financing a vehicle.
- The EPA's ratings are for comparing vehicles, and fueleconomy.gov says they may not accurately predict the average MPG you get. The tool uses the one figure you enter.
- It holds no fuel price of its own; the price is yours to enter.
Sources checked on .