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Fuel Tank Range Calculator

See how far one tank of fuel can take you.

How it is calculated

The usable fuel is the tank size minus the amount you want to keep in reserve, multiplied by fuel economy:

range (mi) = (tank − reserve) × mpg and range (km) = range (mi) × 1.60934

tank and reserve are in gallons and mpg is miles per gallon, so the gallons must be the same kind in all three (US or imperial). The reserve box needs a value: enter 0 if you want to count the whole tank. If the reserve is larger than the tank, the usable fuel is floored at zero and the range is 0. Tank and mpg must be above zero. Results are rounded to whole miles and kilometres. For a car rated in L/100 km you must convert to mpg first.

Worked example

A 14-gallon tank, 30 mpg, with a 2-gallon reserve.

  1. Usable fuel = 14 − 2 = 12 gallons
  2. Range = 12 × 30 = 360 mi
  3. In kilometres: 360 × 1.60934 ≈ 579 km

With no reserve (0) the same tank would show 420 mi.

Try this example →

Common mistakes

  • Entering the tank in litres: the fields are gallons, so 55 litres must be entered as about 14.5 US gallons.
  • Entering L/100 km as mpg: they run in opposite directions, so a lower L/100 km is better but a higher mpg is better.
  • Leaving the reserve blank: the tool then gives no result; type 0 instead.
  • Using the sticker mpg for a long motorway trip with a loaded car, headwind or roof box: real consumption is often worse than the rated figure.

About this calculator

Driving range is simply usable tank capacity × fuel economy — for example a 15-gallon tank at 30 mpg gives roughly 450 miles. You enter the tank size in gallons, the fuel economy in miles per gallon and the reserve in gallons to keep untouched (0 for none), which is subtracted from the tank first; the range is shown in miles and kilometers. If your car is rated in L/100km, convert first: mpg = 235.2 ÷ (L/100km) and gallons = liters ÷ 3.785 — a 55-liter tank at 6 L/100km is about 14.53 gallons at 39.2 mpg, or about 917 km.

Drivers use it to plan long trips and know how far they can go before the next fuel stop, especially on remote highways with sparse gas stations. Fleet managers and road-trip planners also use it to compare how tank size versus efficiency trades off across different vehicles.

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