MPG Calculator
Calculate your car’s miles per gallon fuel efficiency instantly
What is MPG?
Miles Per Gallon (MPG) is the standard measure of fuel efficiency used in the United Kingdom. It represents how many miles a vehicle can travel using one imperial gallon of fuel. A higher MPG figure indicates better fuel efficiency, meaning lower running costs and reduced environmental impact.
In the UK, we use imperial gallons which are larger than US gallons. One imperial gallon equals 4.546 litres, compared to the US gallon which equals 3.785 litres. This means UK MPG figures are typically higher than their US equivalents for the same vehicle.
How to Calculate MPG
Calculating your vehicle’s MPG is straightforward when you know the formula:
If you have fuel consumption in litres, convert to imperial gallons by dividing by 4.546:
Step-by-Step Calculation
- Fill your fuel tank completely
- Reset your trip counter or note your mileage
- Drive normally until you need to refuel
- Note the distance travelled and fuel needed to refill
- Apply the formula: miles divided by gallons used
Fuel Efficiency Benchmarks
Understanding what constitutes good fuel efficiency helps put your MPG results in context:
| Vehicle Type | Excellent MPG | Good MPG | Average MPG | Poor MPG |
|---|---|---|---|---|
| Small Car | 60+ MPG | 45-60 MPG | 35-45 MPG | Below 35 MPG |
| Family Car | 50+ MPG | 40-50 MPG | 30-40 MPG | Below 30 MPG |
| SUV | 45+ MPG | 35-45 MPG | 25-35 MPG | Below 25 MPG |
| Sports Car | 40+ MPG | 30-40 MPG | 20-30 MPG | Below 20 MPG |
Improving Your MPG
Several factors influence your vehicle’s fuel consumption. Small changes to driving habits and vehicle maintenance can significantly improve your MPG:
Driving Technique
Maintain steady speeds, anticipate traffic flow, and avoid sudden acceleration or harsh braking. Smooth driving can improve fuel efficiency by up to 20%.
Speed Management
Most cars achieve optimal fuel efficiency between 45-55 mph. Driving at 80 mph uses approximately 25% more fuel than driving at 70 mph.
Vehicle Maintenance
Regular servicing, proper tyre pressure, and clean air filters can improve MPG by up to 10%. Check tyre pressure monthly and service annually.
Weight Reduction
Remove unnecessary items from your car. Every extra 50kg reduces fuel efficiency by approximately 2%. Clear out boot storage and roof boxes when not needed.
Factors Affecting Fuel Consumption
Multiple variables influence your vehicle’s MPG performance:
Environmental Conditions
- Cold weather reduces fuel efficiency as engines take longer to reach optimal operating temperature
- Headwinds and mountainous terrain increase fuel consumption
- Urban driving with frequent stops uses more fuel than motorway cruising
- Air conditioning can reduce MPG by 5-10% depending on usage
Vehicle Specifications
- Engine size and technology (diesel engines typically achieve higher MPG than petrol)
- Vehicle weight and aerodynamics
- Transmission type (manual vs automatic)
- Tyre type and condition
Frequently Asked Questions
What’s the difference between UK and US MPG?
UK MPG uses imperial gallons (4.546 litres) whilst US MPG uses smaller US gallons (3.785 litres). This means UK MPG figures are approximately 20% higher than US figures for the same vehicle.
How often should I calculate my MPG?
Monitor your MPG monthly to establish baseline performance. Calculate more frequently if you notice changes in fuel costs or suspect mechanical issues affecting efficiency.
Why might my MPG suddenly decrease?
Sudden MPG drops may indicate mechanical problems such as clogged air filters, incorrect tyre pressure, engine issues, or changes in driving patterns. Consider professional inspection if efficiency decreases significantly.
Is manual calculation more accurate than trip computers?
Manual calculation using actual fuel receipts and mileage readings typically provides more accuracy than onboard computers, which may have calibration variations or calculation differences.
Converting MPG to Other Units
Sometimes you may need to convert MPG to other fuel efficiency measurements:
| UK MPG | Litres per 100km | Miles per Litre | US MPG |
|---|---|---|---|
| 30 MPG | 9.4 L/100km | 6.6 MPL | 25 MPG |
| 40 MPG | 7.1 L/100km | 8.8 MPL | 33 MPG |
| 50 MPG | 5.6 L/100km | 11.0 MPL | 42 MPG |
| 60 MPG | 4.7 L/100km | 13.2 MPL | 50 MPG |
References
Department for Transport. (2024). Transport Statistics Great Britain: Energy and Environment. London: HM Stationary Office.
Society of Motor Manufacturers and Traders. (2024). Motor Industry Facts: Fuel Economy Standards. London: SMMT Publications.
RAC Foundation. (2024). Motoring Towards 2030: The Future of Car Use in Britain. London: RAC Foundation.
Energy Saving Trust. (2024). Efficient Driving: A Guide to Eco-Safe Driving. London: Energy Saving Trust Publications.