Fuel economy conversion (MPG ↔ L/100 km)
Watch the direction: lower L/100 km is better, while higher MPG is better — the two scales move opposite ways.
Unit converter
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| US MPG | L/100 km | UK MPG (approx) |
|---|---|---|
| 10 | 23.5 | 12.0 |
| 15 | 15.7 | 18.0 |
| 20 | 11.8 | 24.0 |
| 25 | 9.4 | 30.0 |
| 30 | 7.8 | 36.0 |
| 35 | 6.7 | 42.0 |
| 40 | 5.9 | 48.0 |
| 45 | 5.2 | 54.0 |
| 50 | 4.7 | 60.0 |
| Formula | L/100 km = 235.215 / US_MPG | UK_MPG ≈ US_MPG × 1.201 |
Notes
- UK gallon is larger, so UK MPG reads higher for the same car.
- Electric efficiency uses kWh/100 km or MPGe — different sheet needed.
MPG and L/100 km are inverses of each other
Miles per gallon measures distance per unit of fuel; liters per 100 km measures fuel per unit of distance — the two scales are reciprocals, so one rises as the other falls. The conversion is fixed by two constants: L/100 km = 235.215 / US MPG, and L/100 km = 282.481 / UK MPG. Because the relationship is a division, doubling the MPG halves the consumption, and small MPG changes matter most at the low end. The formula row of the table shows both constants, and the calculator units below use the same inverted factors, so any value maps exactly between the two units.
Who uses which unit — and which direction is better
The United States rates fuel economy in US MPG; the United Kingdom uses imperial MPG (the third column here, "UK MPG (approx)"); most other countries — and every L/100 km figure in this sheet — quote liters per 100 km. The reading direction differs: higher MPG is better, because each gallon carries you farther, while lower L/100 km is better, because you burn less over a fixed distance. Never compare a "good" 30 with a "good" 7.8 directly — they can describe the same efficient car viewed from opposite ends of two inverse scales.
US vs imperial gallon: a ~20% gap
The imperial gallon still used for MPG in the UK holds about 20% more fuel than the US gallon. Since MPG divides distance by gallons, the same car automatically gets a higher number on UK gallons. The table's third column shows the effect: every UK figure is roughly US MPG × 1.201 — 10 becomes 12, 30 becomes 36, 50 becomes 60. Mixing the two without converting inflates apparent economy by about a fifth, so always check which gallon a figure uses before comparing vehicles or spec sheets.
Reading the table: two worked examples
Take 30 US MPG: 235.215 / 30 ≈ 7.8 L/100 km, which is about 36 UK MPG — a genuinely efficient car, the kind a compact hatchback or hybrid achieves. At the other end, 10 US MPG works out to 23.5 L/100 km (12 UK MPG) — typical of a large SUV or heavy truck that burns fuel quickly. Between them the pattern is non-linear: 15 MPG → 15.7, 20 → 11.8, 25 → 9.4 L/100 km. Notice how the L/100 km saving per step shrinks as MPG climbs — that is the inverse scale doing its work.
Frequently asked questions
- How do I convert MPG to L/100 km?
- Divide 235.215 by the US MPG figure: L/100 km = 235.215 / US_MPG. For example, 25 US MPG is about 9.4 L/100 km.
- What is 30 MPG in L/100 km?
- 30 US MPG equals about 7.8 L/100 km, which is roughly 36 UK MPG.
- Why do UK MPG numbers look higher than US MPG?
- The UK (imperial) gallon is about 20% larger than the US gallon, so the same car gets a UK MPG figure about 1.201 times the US one.