Fuel Economy Converter

What is a fuel economy converter?

A fuel economy converter changes a vehicle’s fuel efficiency from one unit into every other unit at once — US miles per gallon (US MPG), UK imperial miles per gallon (UK MPG), litres per 100 kilometres (L/100km) and kilometres per litre (km/L). Enter one figure, pick the unit it is in, and read all the equivalents side by side.

Fuel economy describes how far a vehicle travels on a given amount of fuel, but different regions measure it in different ways. The US and UK both use “miles per gallon,” yet their gallons are different sizes, so the numbers do not match. Most of the world uses L/100km (lower is better) or km/L (higher is better). This tool bridges all four so you can compare cars and quotes accurately, no matter where the numbers came from.

How does the fuel economy converter work?

It converts your input to a single intermediate unit — L/100km — and then derives each other unit from there. Using one pivot unit keeps every conversion consistent and avoids rounding drift from chaining figures.

The core relationships are:

• US MPG ↔ L/100km use the factor 235.215
• UK (imperial) MPG ↔ L/100km use the factor 282.481
• km/L is the reciprocal of distance: km/L = 100 ÷ L/100km

So the primary method is:

L/100km = 235.215 ÷ US MPG

km/L = 100 ÷ (L/100km)

Because MPG and km/L are inverse measures (distance per fuel) while L/100km is a direct measure (fuel per distance), the conversion between MPG and L/100km is a division, not a multiplication. That is why doubling your MPG does not double your L/100km — the relationship is reciprocal.

Units and terms

Unit	Symbol	Measures	Direction
US miles per gallon	US MPG	Distance per US gallon	Higher is better
UK imperial miles per gallon	UK MPG	Distance per imperial gallon	Higher is better
Litres per 100 km	L/100km	Fuel per 100 km	Lower is better
Kilometres per litre	km/L	Distance per litre	Higher is better

The two MPG factors differ only because the imperial gallon (about 4.546 litres) is larger than the US gallon (about 3.785 litres), so a UK MPG figure is always higher than the US MPG figure for the same real-world efficiency.

Examples

Each example below uses the factors above and matches the converter’s output exactly.

Example 1 — 30 US MPG into every unit.

1. To L/100km: 235.215 ÷ 30 = 7.84 L/100km
2. To km/L: 100 ÷ 7.84 = 12.75 km/L
3. To UK MPG: 282.481 ÷ 7.84 = 36.0 UK MPG

So a car rated at 30 US MPG uses about 7.84 litres every 100 km, travels roughly 12.75 km per litre, and would be advertised as about 36.0 MPG in the UK.

Example 2 — 5 L/100km into US MPG.

1. US MPG: 235.215 ÷ 5 = 47.04 US MPG

A very efficient car burning 5 L/100km is equivalent to about 47.04 US MPG.

Example 3 — back the other way, 12.75 km/L into L/100km.

1. L/100km: 100 ÷ 12.75 = 7.84 L/100km

This confirms the reciprocal relationship: 12.75 km/L and 7.84 L/100km describe the same efficiency, which is the same 30 US MPG car from Example 1.

Quick reference table

The table below shows common US MPG values converted with the tool’s exact factors. Use it as a sanity check.

US MPG	L/100km	km/L	UK MPG
20	11.76	8.50	24.02
25	9.41	10.63	30.02
30	7.84	12.75	36.03
40	5.88	17.01	48.04
50	4.70	21.26	60.05

Each L/100km figure is 235.215 divided by the US MPG; km/L is 100 divided by that L/100km; and UK MPG is 282.481 divided by the same L/100km.

What are common uses for a fuel economy converter?

• Comparing cars across regions: match a US window-sticker MPG against a European L/100km rating or a UK MPG brochure figure.
• Importing a vehicle: translate the manufacturer’s home-market efficiency into your local unit before estimating running costs.
• Trip budgeting: convert L/100km to km/L (or MPG) to estimate how far a tank will take you on a long drive.
• Reviewing reviews: car journalists in different countries quote different units; convert them to one unit to compare fairly.
• Fleet and spreadsheet work: standardise mixed data into a single unit before averaging or charting it.

Tips and common mistakes

A few errors trip people up when converting fuel economy:

• Mixing US and UK MPG. They are not the same. A UK MPG figure is always higher for the same car, so comparing a US 30 MPG against a UK 36 MPG without converting makes the UK car look more efficient when they are identical.
• Treating the conversion as a multiplication. MPG to L/100km is a division (235.215 ÷ MPG), because the units are reciprocals. Multiplying gives a wildly wrong answer.
• Assuming higher is always better. Higher is better for MPG and km/L, but for L/100km a lower number is better — it means less fuel used.
• Rounding too early. If you round mid-step and reuse the figure, small errors compound. Keep full precision until the final result; the tool rounds only for display.

Limitations and notes

This converter changes between units of fuel economy only — it does not calculate fuel cost, range, or carbon emissions, and it does not account for driving style, load, terrain or test cycle. Published economy figures (such as EPA, WLTP or NEDC ratings) are measured under different standard conditions, so two ratings in the same unit are not always directly comparable even after conversion.

The factors 235.215 and 282.481 are the standard conversion constants based on the US gallon (3.785 litres) and the imperial gallon (4.546 litres) relative to the mile and kilometre. Results are rounded for a clean display, so the final digit may differ slightly from a hand calculation that keeps more decimal places. For purchasing, regulatory or financial decisions, confirm the official rating and unit from the manufacturer or testing authority.

For related unit work, try the length converter for the distance side, the speed converter for km/h and mph, and the weight converter for mass. Browse more on the converters category page.