General

Fuel Consumption Calculator

Work out your real-world MPG, km/L or L/100km, or convert between any of those units instantly.

I just filled up Unit converter

Distance traveled

Distance unit

Fuel used

Fuel unit

Fuel economy

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Enter distance and fuel used.

What this calculator does

Two tools in one. The first works out the fuel economy of your last tank: enter distance and fuel used and you get MPG, km/L and L/100km side by side. The second is a pure unit converter for moving between any of those four units, including the difference between US and UK gallons.

How to use it

After a fill-up, reset your trip meter on the previous fill. Drive normally, fill up again to the same click, then enter the trip distance and the liters or gallons added. The calculator does the rest. For the converter, pick the unit you have, type the number, and the other three units update live.

The formulas

MPG (US) = miles ÷ US gallons. km/L = km ÷ liters. L/100km = (liters ÷ km) × 100. 1 US gallon = 3.7854 L, 1 UK gallon = 4.5461 L, 1 mile = 1.60934 km. So MPG (US) ≈ 235.215 ÷ L/100km.

Quick reference

L/100km	km/L	MPG (US)	MPG (UK)
4	25.00	58.8	70.6
5	20.00	47.0	56.5
6	16.67	39.2	47.1
7	14.29	33.6	40.4
8	12.50	29.4	35.3
10	10.00	23.5	28.2
12	8.33	19.6	23.5
15	6.67	15.7	18.8
20	5.00	11.8	14.1

Frequently asked questions

What is the difference between US and UK MPG?

A US gallon is 3.7854 liters and a UK gallon is 4.5461 liters, about 20% larger. So 30 MPG (US) is about 36 MPG (UK) for the same physical fuel use. Always check which gallon a number refers to before comparing cars across markets.

Is L/100km better than MPG?

L/100km is linear: doubling the number means twice the fuel. MPG is the inverse, so improving from 20 to 25 MPG saves much more fuel than improving from 40 to 45 MPG. Most engineers and European regulators use L/100km for that reason.

Why is my real MPG lower than the EPA sticker?

Sticker values come from a controlled lab test that does not include very cold weather, full passenger loads, roof boxes, aggressive driving or short trips. Real-world numbers 10 to 20% below sticker are normal.

How do I convert MPG to L/100km in my head?

Use the rule 235 ÷ MPG (US). So 30 MPG ≈ 7.8 L/100km, 40 MPG ≈ 5.9 L/100km. The same trick works the other way: 235 ÷ L/100km gives you MPG (US).

Should I use trip-meter distance or odometer?

The trip meter, reset at the last fill-up, is the most accurate. The odometer requires you to subtract two readings and any rounding error in either reading goes straight into your MPG number.

Does this work for diesel?

Yes. The math is identical for any liquid fuel: distance divided by volume. The only thing diesel changes is energy density, which affects fuel economy in the real world but not the math behind the conversion.

Fuel Consumption Calculator