Fuel Economy Calculator & Guide
Instantly convert between UK MPG, US MPG, and L/100km, and estimate your total fuel costs and consumption for any journey.
Calculate Your Fuel Costs
Enter your journey distance, vehicle efficiency, and current fuel prices below to instantly estimate your total fuel consumption and trip cost.
Trip Fuel Cost Estimator
Get accurate consumption and cost breakdowns.
Improve Your Fuel Economy
Simple habits to save money at the pump
Check Tyre Pressure
Under-inflated tyres increase rolling resistance. Keeping them at the manufacturer’s recommended pressure can improve mileage by up to 3%.
Reduce Excess Weight
An extra 100 pounds (45 kg) in your vehicle can reduce your MPG by up to 1%. Remove heavy, unnecessary items from your boot.
Use Cruise Control
On flat motorways, cruise control helps you maintain a constant speed, which prevents the subtle acceleration and deceleration that wastes fuel.
Regular Servicing
A tuned engine, clean air filters, and the correct grade of motor oil ensure your engine operates at peak efficiency, maximising every drop of fuel.
MPG to L/100km Conversion
Standardised conversions between UK MPG, US MPG, and Litres per 100 Kilometres.
| UK MPG | US MPG | Litres / 100km | Efficiency Rating |
|---|---|---|---|
| 16.7 | 14.1 | Poor (Large SUVs / Older vehicles) | |
| 25.0 | 9.4 | Below Average | |
| 33.3 | 7.1 | Average (Modern Petrol/Diesel) | |
| 41.6 | 5.6 | Good (Efficient Hatchbacks) | |
| 49.9 | 4.7 | Excellent (Modern Hybrids) | |
| 58.3 | 4.0 | Outstanding (Plug-in Hybrids / Diesel) | |
| 83.3 | 2.8 | Exceptional (Ultra-efficient Diesels) |
Fuel Economy FAQ
Answers to the most frequently asked questions about fuel efficiency, conversions, and saving money on petrol and diesel.
To convert UK MPG to L/100km, divide 282.48 by the MPG value. For example, 40 MPG (UK) is equal to 7.06 L/100km (282.48 / 40). For US MPG, divide 235.21 by the MPG value.
A good fuel economy for a standard petrol or diesel car is generally considered to be over 45–50 MPG (UK), or roughly 5.0–6.0 L/100km. Hybrid vehicles often exceed 60 MPG, while electric vehicles are measured in miles per kWh instead.
The UK uses the Imperial gallon (4.546 litres), while the US uses the US liquid gallon (3.785 litres). Because the UK gallon is larger, a car will show a higher MPG figure in the UK than in the US for the exact same fuel efficiency. 40 UK MPG is approximately 33.3 US MPG.
You can improve fuel economy by maintaining correct tyre pressure, removing unnecessary weight from the vehicle, avoiding aggressive acceleration and heavy braking, using cruise control on motorways, and ensuring regular engine servicing.
Yes. Running the air conditioning puts an extra load on the engine, which can reduce fuel economy by up to 10–20% in very hot conditions. At low speeds, opening windows is more efficient, but at motorway speeds, the aerodynamic drag from open windows can use more fuel than the AC.