Fuel Distance Calculator

Background.

Range on a tank is simple arithmetic — gallons times miles per gallon — and yet people still run dry, usually on the stretch of road where the next station turned out to be closed. The trouble is rarely the multiplication. It is planning to the last drop with an mpg figure that was optimistic to begin with.

This page builds a margin into the answer. You say how much fuel is on board, what economy you expect, and what share of that fuel you refuse to count on. The reserve comes off first; only the remaining gallons are turned into miles. With 12 gallons, 30 mpg and a 10% reserve, you plan on 324 miles rather than 360, and the 36-mile difference is the cushion that absorbs a headwind, a detour or a gauge that reads a little high.

The economy figure deserves more thought than the fuel figure. The most honest number is one you have measured yourself: fill the tank, reset the trip meter, drive normally, refill, and divide miles driven by gallons added. Window-sticker ratings are tested under standard cycles that may not match your driving, and real economy moves with speed, air conditioning, cargo, roof boxes, cold starts and towing. None of those are modelled here; they enter only through the mpg you type in.

One detail is easy to miss. The reserve is a percentage of the fuel you enter, not of the tank's capacity. Start a trip with half a tank and a 10% reserve holds back half as many gallons as it would on a full one, so on long empty roads with a part-filled tank, a larger percentage is the safer choice.

What is fuel distance calculator?

Fuel distance is the mileage a vehicle can cover on a given quantity of fuel at a given rate of consumption. Here it is computed net of a reserve: a fixed percentage of the fuel on board that is set aside and never converted into planned miles. The answer is in miles, and it assumes the economy you enter holds steady for the whole distance, which in practice it only does approximately.

How to use this calculator.

1. 01Enter the usable fuel on board in gallons — the amount actually in the tank, not its rated capacity. If you have just filled up, the gallons on the pump receipt plus whatever was left in the tank is a fair figure.
2. 02Enter the fuel economy you expect for this trip. A figure measured from your own fill-to-fill records beats a published rating; lower it if you will be towing, carrying a heavy load or cruising fast.
3. 03Make sure the gallon in both fields is the same gallon: US gallons with US mpg, or imperial gallons with UK mpg. Mixing them misstates the range by about 20%.
4. 04Set the reserve percentage. The default 10% suits roads where stations are frequent; raise it for remote routes, night driving or a part-filled tank.
5. 05Read the distance after reserve as the furthest point you should plan to reach, and the reserved fuel as the gallons you are keeping in hand.

The formula.

Distance = fuel × (1 − reserve ÷ 100) × mpg. The bracket turns the reserve percentage into the fraction of fuel you are willing to use: a 10% reserve leaves 0.9 of the tank, a 25% reserve leaves 0.75. Multiplying that fraction by the fuel gives the gallons available for planning, and multiplying those gallons by miles per gallon gives miles. The reserved fuel shown alongside is simply the fuel entered minus the usable part. Because every term multiplies, the result is proportional to each one: a 10% error in your mpg figure moves the distance by exactly 10%, which is usually a bigger effect than any sensible change to the reserve. A reserve of 100% or an economy of zero returns zero miles.

A worked example.

Frequently asked questions.

References& sources.

1. [1]U.S. Department of Energy. Energy Saver current 2026. Household energy guidance. Retrieved 2026-08-06.
2. [2]National Institute of Standards and Technology. NIST SI Guide, 2008 edition. Appendix B unit relationships. Retrieved 2026-08-06.
3. [3]OpenStax, Rice University. University Physics, 2016. Volume 1 mechanics and Volume 2 thermodynamics. Retrieved 2026-08-06.