Fuel Economy Calculator
Convert MPG to L/100km, calculate journey fuel cost, and compare your car's efficiency against UK benchmarks.
MPG / Fuel Economy Converter
MPG (UK)
40
L/100km
7.06
km/L
14.16
Journey Fuel Cost
Fuel Used
11.37 L
2.5 gal
Journey Cost
£16.82
at 148p/L
Cost per Mile
£0.168
per mile
UK Car Fuel Economy Benchmarks
| Car Type | MPG (UK) | L/100km |
|---|---|---|
| Small city car (e.g. VW Polo) | 50 | 5.7 |
| Family hatchback (e.g. Ford Focus) | 40 | 7.1 |
| Family saloon (e.g. BMW 3 Series) | 35 | 8.1 |
| Large SUV (e.g. Range Rover) | 22 | 12.8 |
| Electric vehicle (equivalent) | 100 | 2.8 |
| Hybrid (e.g. Toyota Prius) | 60 | 4.7 |
Key Facts
UK MPG uses imperial gallons (4.546L)
US MPG uses US gallons (3.785L) — 20% less
EU uses L/100km (lower = more efficient)
Average UK car: ~35–40 MPG
DVLA fuel economy figures are tested under ideal conditions
UK MPG vs European L/100km — What's the Difference?
The UK measures fuel economy in miles per gallon (MPG), where a higher number means better efficiency. Europe uses litres per 100 kilometres (L/100km), where a lower number means better efficiency. This can cause confusion when comparing cars across markets. A car rated at 40 MPG (UK) is equivalent to approximately 7.1 L/100km.
Importantly, UK MPG is not the same as US MPG. The UK uses the imperial gallon (4.546 litres), while the US uses the smaller US gallon (3.785 litres). This means a car rated at 40 UK MPG would only achieve approximately 33 US MPG — a difference of about 20%. Always check which standard is being used when comparing international car reviews.
Real-world fuel economy is typically 10–20% lower than the official manufacturer figures, which are measured under controlled laboratory conditions. Factors such as driving style, road type, air conditioning use, tyre pressure, and load all affect actual fuel consumption. Using this calculator with your real-world MPG figure will give you a more accurate journey cost estimate.