How do I calculate fuel cost for a trip?

Divide the distance by your car's MPG to get gallons, then multiply by the price per gallon. In metric, multiply km by L/100km, divide by 100, then multiply by the price per litre.

How much gas will I use for 100 miles?

100 divided by your MPG. At 25 MPG that's 4 gallons; at 40 MPG it's 2.5 gallons.

Should I use the EPA MPG or my own?

Your own logged MPG is more accurate for your driving. EPA ratings are useful for comparing cars, but real results vary with speed, traffic and weather.

How do I split gas money between friends?

Calculate the total fuel cost for the trip and divide by the number of people sharing. Some groups exclude the driver; that's up to you.

Why is UK MPG higher than US MPG?

A UK (imperial) gallon is about 4.55 litres while a US gallon is about 3.79 litres, so the same car travels further per UK gallon.

Fuel Cost Calculator: Trip Gas Cost (2026) / CarO

Written by Muneeb Rana · Last updated 21 October 2026

Quick answer: A fuel cost calculator multiplies trip distance by your car's fuel use and the fuel price. In US units: cost = miles ÷ MPG × price per gallon. In metric: cost = km × L/100km ÷ 100 × price per litre. For a 300-mile trip at 30 MPG and $3.15 a gallon, that's 10 gallons, about $31.50.

TL;DR

Enter distance, fuel economy and fuel price.
Toggle round trip and split the cost between passengers.
Use your real logged economy, not the sticker figure, for the best estimate.

This fuel cost calculator works out the cost of any drive: a commute, a road trip or a month of driving. It uses your car's fuel economy and current fuel price, works in miles or kilometres, and can split the cost between passengers. It also covers trip cost questions, so our old trip-cost tool now redirects here.

How to use the fuel cost calculator

Choose units: miles and MPG (US or UK gallons), or kilometres and L/100km or km/L.
Enter the distance, or start and end odometer readings.
Enter your car's fuel economy. Your own logged figure is more accurate than the EPA label.
Enter the fuel price. AAA publishes the US average daily.
Tick round trip, and enter how many people are sharing the cost.

How the fuel cost calculator works

gallons = miles / mpg
cost    = gallons * price_per_gallon
metric: litres = km * l_per_100km / 100 ; cost = litres * price_per_litre
round trip doubles distance; per person = cost / people

UK MPG uses imperial gallons (4.546 L) rather than US gallons (3.785 L), so the same car shows a higher MPG figure in the UK. The tool converts automatically; see the fuel economy converter.

Worked example

A 300-mile round trip (600 miles) in a car that averages 30 MPG uses 20 gallons. At $3.15 a gallon (close to AAA's 2025 average regular price used in its cost study), fuel costs about $63, or $21 each for three people.

Make the estimate more accurate

Real-world economy varies with speed, traffic, loads and weather. FuelEconomy.gov notes that aggressive driving can cut highway economy by 15-30%, and that each 5 mph above 50 mph is like paying about $0.30 more per gallon. A roof box can reduce economy by 2-8% in city driving and more on highways. Logging fill-ups for a few weeks in a fuel log gives you your true figure; the MPG calculator shows how.

Fuel cost per mile

Divide price per gallon by MPG: $3.15 ÷ 30 MPG = 10.5 cents per mile. AAA's 2025 study used 13 cents per mile for fuel on an average new car. Add maintenance and other costs with the cost of car ownership calculator.

Driving electric?

Use the EV charging cost calculator instead. For ways to spend less on fuel, read how to improve fuel economy.

Download CarO free on the App Store or Google Play. Free with ads; optional in-app purchases.

Sources

FuelEconomy.gov: Driving More Efficiently: www.fueleconomy.gov (accessed 21 October 2026)
AAA: Gas Prices: gasprices.aaa.com (accessed 21 October 2026)
AAA: Your Driving Costs 2025 fact sheet: newsroom.aaa.com (accessed 21 October 2026)
FuelEconomy.gov: Find and Compare Cars: www.fueleconomy.gov (accessed 21 October 2026)

Disclaimer: CarO and this website give general car-care information, not professional advice. Maintenance intervals and specifications vary by vehicle, so always follow your owner's manual and a qualified mechanic. Mileage and cost figures are estimates; check local tax rules before using any log for deductions.

Fuel Cost Calculator for Any Trip