How this fuel economy converter works
Fuel economy is described in two opposite ways. Distance-per-fuel units — MPG (miles per gallon) and km/L (kilometres per litre) — go up as a vehicle gets more efficient. Fuel-per-distance units — L/100km (litres per 100 kilometres) — go down as a vehicle gets more efficient. Because MPG and L/100km are inverse of each other, you cannot simply add or scale between them; this tool converts everything through a single linear base (kilometres per litre) so the results stay accurate.
The exact factors used are: 1 US gallon = 3.785411784 L, 1 Imperial gallon = 4.54609 L and 1 mile = 1.609344 km. From those: L/100km = 235.215 ÷ MPG (US), L/100km = 282.481 ÷ MPG (Imperial), and km/L = MPG (US) × 0.425144. The most-searched pairing — MPG (US) to L/100km — is highlighted at the top so you can read it at a glance.
Common conversions
| From | Equals |
|---|---|
| 30 MPG (US) | 7.84 L/100km |
| 40 MPG (US) | 5.88 L/100km |
| 1 MPG (US) | 1.20 MPG (Imperial) |
| 1 km/L | 2.352 MPG (US) |
Reference note: 235.215 comes from 100 × 3.785411784 ÷ 1.609344, and 282.481 from 100 × 4.54609 ÷ 1.609344. Results are rounded for readability, so very small differences in the last decimal are normal. L/100km is undefined when MPG or km/L is 0, because a stationary or non-moving vehicle has no distance to divide by.
Frequently asked questions
- How do I convert MPG to L/100km?
- Divide 235.215 by the MPG (US) figure to get litres per 100 km. For example, 30 MPG (US) gives 235.215 ÷ 30 ≈ 7.84 L/100km. The same formula works in reverse: L/100km = 235.215 ÷ MPG, and MPG = 235.215 ÷ (L/100km).
- Why are MPG and L/100km inverse measures?
- MPG measures distance per fixed fuel (miles per gallon), so a bigger number is better. L/100km measures fuel per fixed distance (litres per 100 km), so a smaller number is better. Because one is distance-over-fuel and the other is fuel-over-distance, they move in opposite directions — doubling your MPG roughly halves your L/100km.
- What is the difference between US and Imperial MPG?
- They use different gallons. A US gallon is 3.785411784 litres, while an Imperial (UK) gallon is 4.54609 litres — about 20% larger. So the same car shows a higher number in Imperial MPG than in US MPG. 30 MPG (US) is roughly 36 MPG (Imperial).
- What is km/L (kilometres per litre)?
- Kilometres per litre is how far a vehicle travels on one litre of fuel. Like MPG, a higher number is better. To convert from MPG (US), multiply by 0.425144; for example 30 MPG (US) × 0.425144 ≈ 12.75 km/L.
- Is a lower L/100km better?
- Yes. L/100km is the amount of fuel used to drive 100 km, so using fewer litres means the vehicle is more efficient. A car that returns 5 L/100km is more economical than one returning 9 L/100km.
- What counts as good fuel economy?
- As a rough guide, around 6 L/100km (about 39 MPG US or 47 MPG Imperial) is good for a petrol car, and under 5 L/100km is excellent. Hybrids and efficient diesels often do better. Figures vary with vehicle size, driving style and conditions.