Fuel Efficiency Calculator — L/100km, km/L and MPG
Fill up, drive, fill up again — enter the distance and litres used to get your real-world economy in four units. Real-world figures often differ from brochure values, and this is the way to measure yours.
Fuel Efficiency
L/100km, MPG and km per liter
How it works
- L/100km = litres ÷ distance × 100 (lower is better).
- MPG US and MPG UK differ because the gallons differ.
- km/L is the inverse view: higher is better.
- Measure over several tanks for a reliable average — one tank can be misleading.
Worked example: 512 km on 38.4 litres
- 1L/100km: 38.4 ÷ 512 × 100 = 7.5.
- 2km/L: 512 ÷ 38.4 = 13.3.
- 3MPG US: 235.2 ÷ 7.5 ≈ 31.4; MPG UK ≈ 37.7.
7.5 L/100km · 13.3 km/L · 31.4 MPG (US)
Fuel economy conversion reference
| L/100km | km/L | MPG (US) | MPG (UK) |
|---|---|---|---|
| 4.0 | 25.0 | 58.8 | 70.6 |
| 5.0 | 20.0 | 47.0 | 56.5 |
| 6.0 | 16.7 | 39.2 | 47.1 |
| 7.5 | 13.3 | 31.4 | 37.7 |
| 9.0 | 11.1 | 26.1 | 31.4 |
| 12.0 | 8.3 | 19.6 | 23.5 |
Frequently asked questions
Is 7 L/100km good?
For a petrol family car, yes — that is roughly 34 MPG US and 40 MPG UK.
How do I convert L/100km to MPG?
Divide 235.2 by the L/100km figure for US MPG, or 282.5 for UK MPG. For 8 L/100km: 235.2 ÷ 8 ≈ 29.4 MPG (US).
Why is my real consumption higher than the official figure?
Official test cycles are gentler than real driving. Cold starts, short trips, motorway speeds, air conditioning and roof racks all push real-world use up, often by 15–30%.
How can I improve my fuel economy?
Keep tyres at the right pressure, remove roof racks, accelerate gently, anticipate traffic to avoid braking, and stick near 90–100 km/h on motorways.
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