Fuel Economy Converter

Convert a fuel economy figure between L/100km, mpg (US), mpg (UK), and km/L. Pick the unit you have and enter the value — every other unit updates automatically.

L/100km8 L/100km

mpg (US)29.4 mpg (US)

mpg (UK)35.3 mpg (UK)

km/L12.5 km/L

How this calculation works

L/100km and km/L both measure fuel per distance (or distance per fuel) using litres, so converting between them is a simple division: km/L = 100 ÷ (L/100km).

mpg is distance per volume, the inverse relationship of L/100km. The conversion constant depends on the gallon: mpg (US) = 235.214583 ÷ (L/100km), and mpg (UK) = 282.480936 ÷ (L/100km), because a US gallon (3.785 L) is smaller than an imperial UK gallon (4.546 L).

This calculator normalizes whatever you enter to L/100km internally, then derives the other three units from that single normalized value so every conversion stays consistent.

Worked example

A car rated at 8 L/100km converts to about 29.4 mpg (US), 35.3 mpg (UK), and 12.5 km/L. Note how the mpg (UK) figure is meaningfully higher than mpg (US) for the exact same real-world fuel use — that gap trips people up when comparing US and UK/Irish car reviews.

Quick reference: common fuel economy figures

A rough sense of where typical vehicles land across all four units:

L/100km	mpg (US)	mpg (UK)	km/L	Typical vehicle
4.0	58.8	70.6	25.0	Efficient hybrid
6.0	39.2	47.1	16.7	Efficient compact car
8.0	29.4	35.3	12.5	Average mid-size sedan
10.0	23.5	28.2	10.0	SUV / crossover
14.0	16.8	20.2	7.1	Large truck / older SUV

US gallon vs UK (imperial) gallon

US gallon = 3.785 litres — used for mpg (US), common in the United States.
UK (imperial) gallon = 4.546 litres — used for mpg (UK), common in the United Kingdom, Ireland, and older Commonwealth references.
A UK gallon is about 20% larger than a US gallon, so mpg (UK) figures are always noticeably higher than mpg (US) figures for identical fuel consumption.
L/100km and km/L are gallon-free and unambiguous, which is why most of the world (and most international comparisons) uses them instead of mpg.

Why this matters when buying or importing a car

Fuel economy ratings printed on a window sticker, spec sheet, or online listing are not automatically comparable across markets. A car imported from the US will quote mpg (US); a UK dealer listing quotes mpg (UK); most of continental Europe, Korea, and Japan quote L/100km or km/L. Converting to one common unit before comparing prevents you from under- or over-estimating a car's actual efficiency — a mistake that's easy to make since both figures are simply labelled "mpg".

The same logic applies to planning fuel costs for a road trip: pairing this converter with a fuel-cost calculator lets you budget in whatever unit your car's trip computer or a foreign fuel pump actually displays.

Frequently asked questions

Why is mpg (UK) higher than mpg (US) for the same car?

Because the UK (imperial) gallon holds more fuel — about 4.546 litres versus 3.785 litres for a US gallon. Since mpg measures distance per gallon, the larger UK gallon produces a bigger mpg number for identical real-world fuel consumption. A US gallon is roughly 83% of a UK gallon.

Is lower or higher better?

For L/100km, lower is better — it means less fuel burned per 100 kilometres. For mpg and km/L, higher is better, since both measure distance travelled per unit of fuel. Keep this in mind: they run in opposite directions.

Why does a US car spec sheet show a different mpg than a UK review of the same model?

They are almost certainly using different gallons, not different test data. Always check whether an mpg figure is US or UK before comparing, and convert to a common unit like L/100km if in doubt.

How accurate is this conversion?

The conversion itself is an exact unit conversion, not an estimate — the mpg and km/L numbers only differ from the source L/100km figure due to rounding at display precision. The underlying fuel economy rating (from the manufacturer or test cycle) is only as accurate as that original test.

Does this account for driving style or real-world conditions?

No. This tool only converts units; it does not adjust for driving style, terrain, load, or climate. Official ratings (WLTP, EPA, etc.) and real-world fuel economy often differ, sometimes by 10–20%, regardless of which unit you use.

Is my data stored or sent anywhere?

No. The conversion happens entirely in your browser and nothing you enter is transmitted, logged, or saved.

Why would I need to convert fuel economy at all?

It matters most when comparing cars across markets — importing a vehicle, reading a foreign review, or comparing a US-spec car (mpg US) to a European one (L/100km) — or when budgeting road-trip fuel costs using a rating quoted in a unit your fuel gauge or trip computer doesn't use.

This tool is provided for general information only. Verify important figures independently. · Last reviewed: August 25, 2026