Convert MPG and L/100km
Type into either field. These are inverse measures of the same thing — one counts distance per fuel, the other counts fuel per distance — which is why the same constant, 235.215, converts both directions.
| Typical economy | MPG (US) | L/100km | Where you see it |
|---|---|---|---|
| 15 mpg | 15 | 15.7 | Full-size truck, towing |
| 20 mpg | 20 | 11.8 | Full-size SUV |
| 25 mpg | 25 | 9.4 | Midsize sedan |
| 35 mpg | 35 | 6.7 | Compact car |
| 45 mpg | 45 | 5.2 | Hybrid sedan |
| 55 mpg | 55 | 4.3 | Efficient hybrid, highway |
Want cost per mile and trip cost too? The MPG and fuel cost calculator starts from a real fill-up and works out what your driving actually costs.
Getting a number you can act on
- 01Type into whichever field matches your source
US and Canadian figures are usually MPG; European and most international figures are L/100km. The other field converts automatically.
- 02Remember the relationship is inverted, not linear
A lower L/100km is better economy, same as a higher MPG is better economy — the scales point in opposite directions, which trips people up when scanning a table quickly.
- 03Don't judge an MPG change by how big the number looks
Going from 15 to 20 MPG saves far more fuel over a fixed distance than going from 30 to 35 MPG, even though both are a 5 MPG improvement. The table below shows why.
- 04Confirm which gallon is being used
This converter uses the US gallon. A UK (imperial) gallon is about 20% larger, so a figure quoted in UK MPG needs an extra conversion step before this applies directly.
What the calculator is actually doing
Nothing here is proprietary. If you would rather check it by hand, or explain it to someone at a counter, these are the same expressions the tool evaluates.
L/100km = 235.215 ÷ MPGThe constant folds together US gallons, litres, miles and kilometres into one figure.
MPG = 235.215 ÷ L/100kmReciprocal measures use the same constant in both directions — that symmetry is a genuine property of the relationship, not a coincidence.
Why equal MPG gains are not equal fuel savings
This is the single most useful thing to understand about MPG, and converting to L/100km makes it visible immediately.
MPG measures distance per fuel, which means it is a rate written upside down from what actually costs money — fuel per distance. Improving from 15 to 20 MPG on a 12,000-mile year saves 200 gallons. Improving from 30 to 35 MPG over the same distance saves only 57 gallons, despite both being a 5 MPG jump.
L/100km avoids this distortion because it already measures fuel per distance directly. Equal improvements in L/100km represent genuinely equal fuel savings, which is exactly why the rest of the world settled on it as the standard unit and why it is worth converting to whenever you are comparing improvements rather than absolute figures.
MPG to L/100km Converter FAQ
How do I convert MPG to L/100km?+
Divide 235.215 by the MPG figure. So 30 MPG converts to about 7.84 L/100km.
How do I convert L/100km to MPG?+
Divide 235.215 by the L/100km figure — the same constant works in both directions. So 8 L/100km converts to about 29.4 MPG.
Why does the same number convert both ways?+
Because MPG and L/100km are reciprocal measures of the same thing. One counts distance per fuel, the other fuel per distance, and that reciprocal relationship is why a single constant divides into either one.
Is 8 L/100km good fuel economy?+
It converts to about 29.4 MPG, which is reasonable for a midsize vehicle. Whether it counts as good depends on the vehicle class — a compact car doing 8 L/100km would be considered thirsty.
Does this use the US or UK gallon?+
The US gallon. A UK (imperial) gallon is about 20% larger, so a UK MPG figure needs converting to US MPG, or to L/100km directly, before comparing against a US-sourced number.
Standards and references behind these figures
The arithmetic on this page is fixed, but the boundaries and conventions around it come from published standards and manufacturer guidance. These are the documents they come from, so you can check them rather than take them on trust.
01US EPA — fuel economy and EV range testingThe five-cycle test procedure behind every window-sticker MPG figure.↗0240 CFR 600.210-12 — calculation of fuel economy values for labelingThe regulation that defines how city and highway results are weighted into the combined figure.↗Convert, then check the tolerance. A converted figure is exact, but the specification it came from was not. Torque specs carry a tolerance and pressure figures are stated cold, so rounding to a value your tool can actually set is normally fine — provided you know which way you rounded and by how much.