Fuel Distance Calculator (how far can I drive on the fuel left?)

Understanding the fuel range calculator — concept and principle

This calculator estimates how far you can drive on the fuel left in your tank, with and without keeping a reserve, from your car's fuel economy. It is useful when the warning light comes on, when planning the next fuel stop on a remote road, or when checking whether a trip is possible without refuelling.

How far the tank goes: with the default inputs the result is 156 km (≈ 97 miles to empty).

How it is calculated

Fuel is converted to litres (US gallon = 3.785411784 L, UK gallon = 4.54609 L).
Fuel economy is converted to litres per 100 km: km/L → 100 ÷ value; US mpg → 235.215 ÷ value; UK mpg → 282.481 ÷ value.
Range (km) = litres ÷ (L/100 km) × 100; miles = km ÷ 1.609344.
Range keeping a reserve = (fuel left − reserve) converted the same way.

The principle

Range is simply the fuel you have divided by how much fuel each kilometre uses. The units need care: L/100 km is fuel per distance, while km/L and mpg are distance per fuel, so converting between them takes a reciprocal. A reserve is fuel you decide not to use, so it is taken off before dividing. Keeping a reserve matters because consumption is never constant: hills, headwinds, traffic and cold engines all use more fuel than the average, and running a tank completely dry can damage some fuel pumps and leave you stranded.

Worked example

Default inputs: 12 litres left, 13 km/L, reserve 3 litres.

Fuel = 12 litres; consumption = 100 ÷ 13 = 7.69 L/100 km.
Range = 12 ÷ 7.692 × 100 = 156 km, shown as 156 km (97 miles).
With reserve: (12 − 3) = 9 L ÷ 7.692 × 100 = 117 km (73 miles).

Each point is the calculator re-run with only “Fuel left in the tank” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Fuel left in the tank	Distance you can drive (km)
3	39
6	78
9	117
12	156
15	195
18	234
24	312

How to read the result

Plan to refuel within the "keeping the reserve" distance, not the full range. The full range assumes your average consumption holds right to the last drop, which is optimistic on motorways, in cold weather or with a heavy load. Many cars' fuel gauges and trip computers are also approximate near empty, so do not rely on them to the last kilometre.

Common mistakes

Using the brochure fuel economy instead of your real-world average.
Mixing US and UK gallons.
Setting the reserve to zero on a road with few fuel stations.
Forgetting that air-conditioning, roof boxes and towing raise consumption.

Keep in mind: The result is an estimate. Fuel gauges, real consumption and road conditions vary; refuel early on unfamiliar or remote routes.

Frequently asked questions

How far can I drive on 10 litres?

Divide by your consumption: at 7.5 L/100 km it is about 133 km.

How far can I go after the fuel light comes on?

It depends on the car's reserve and your consumption; check the owner's manual and refuel as soon as you can.

How do I convert km/L to L/100 km?

Divide 100 by the km/L figure; 13 km/L is about 7.69 L/100 km.

Sources: NIST Special Publication 811 (2008), Appendix B (1 mile = 1.609344 km; 1 US gallon = 3.785411784 L; 1 UK gallon = 4.54609 L)

Checked 9 Nov 2026. Exact unit definitions from NIST SP 811 (2008), Appendix B: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 UK gallon = 4.54609 L.

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