Truck MPG Calculator

Calculate truck fuel economy in MPG from miles and gallons or odometer readings, with fuel cost per mile, L/100 km and yearly savings from better MPG.

Fuel is one of the biggest costs of running a truck, and MPG is the number that drives it. This calculator works out fuel economy from miles and gallons — or from two odometer readings — then converts it to fuel cost per mile and litres per 100 km, and shows what a better MPG would save over a year.

How to use this tool

Choose whether to enter trip miles or start and end odometer readings.
Enter the gallons it took to refill the tank after the trip.
Enter the price you paid per gallon.
Enter your yearly miles and a target MPG to see the value of the difference.

Formula

MPG = Miles driven ÷ Gallons used

Fuel cost per mile = Price per gallon ÷ MPG

L/100 km = 235.215 ÷ MPG

235.215 converts US miles per gallon to litres per 100 km, from 1 US gallon = 3.785411784 L and 1 mile = 1.609344 km. Fill the tank to the same point at the start and the end so the gallons match the miles.

Example

A truck covers 1,200 miles on 185 gallons: 1,200 ÷ 185 = 6.49 MPG, or about 36.3 L/100 km. At $3.85 a gallon the trip used $712.25 of fuel, about $0.59 a mile. Over 100,000 miles a year that comes to about $59,354; at 7.0 MPG it would be $55,000, a saving of roughly $4,354 a year.

Frequently asked questions

Why is my dashboard MPG different?

Dashboard estimates and measured refills can differ because of sensor assumptions, pump cutoff, vehicle angle and fuel expansion. Use consistent full-to-full measurements over several fills to reduce random variation.

Should idle fuel count?

Yes, if you want your real cost per mile. Idling burns fuel without adding miles, so including it lowers MPG — and that lower figure is the true one for budgeting.

How can I improve truck MPG?

Reducing unnecessary idling reduces fuel consumed without covering distance. Track comparable routes, payload and weather over several fills; a single trip cannot isolate the effect of an equipment or driving change.

Sources

Last updated: 2026-10-30