MPG Calculator
Quick Tip: Fill your tank completely, reset your trip metre, then drive normally until your next fill-up. Record the distance and fuel amount for the most accurate calculation.
Current Average UK Fuel Prices (2024): Petrol approximately 145-150p/litre, Diesel approximately 150-155p/litre
Vehicle 1
Vehicle 2
How to Calculate MPG
Miles per gallon (MPG) measures how efficiently your vehicle uses fuel. A higher MPG indicates better fuel economy and lower running costs.
Step-by-Step Method
- Fill your fuel tank completely until the pump stops automatically
- Reset your trip metre to zero or note your current odometer reading
- Drive normally until you need to refuel (ideally when the tank is at least half empty)
- Fill the tank completely again and record the fuel amount added
- Note the distance travelled since the last fill-up
- Use the calculation formulae below to determine your MPG
Calculation Formulae:
MPG (Imperial) = Miles Travelled ÷ Gallons Used
MPG (from litres) = Miles Travelled ÷ (Litres Used ÷ 4.546)
L/100km = (Litres Used ÷ Kilometres Travelled) × 100
MPG (Imperial) = Miles Travelled ÷ Gallons Used
MPG (from litres) = Miles Travelled ÷ (Litres Used ÷ 4.546)
L/100km = (Litres Used ÷ Kilometres Travelled) × 100
Important: Imperial gallons (UK) are different from US gallons. One Imperial gallon equals 4.546 litres, whilst one US gallon equals 3.785 litres. Always use Imperial gallons for UK vehicles.
Typical MPG Values by Vehicle Type
| Vehicle Type | Petrol MPG Range | Diesel MPG Range |
|---|---|---|
| Small Car (e.g., Fiesta, Corsa) | 45-55 MPG | 55-70 MPG |
| Medium Car (e.g., Focus, Golf) | 40-50 MPG | 50-65 MPG |
| Large Car (e.g., Mondeo, Passat) | 35-45 MPG | 45-60 MPG |
| SUV/Crossover | 30-40 MPG | 40-50 MPG |
| Hybrid Vehicle | 50-70 MPG | 60-80 MPG |
| Performance Car | 25-35 MPG | 35-45 MPG |
These figures represent typical combined (urban and motorway) fuel consumption. Actual MPG varies based on driving style, conditions, and vehicle maintenance.
Factors Affecting Fuel Economy
Driving Habits
- Aggressive acceleration: Rapid acceleration can reduce MPG by up to 33% on motorways
- Excessive speed: Driving at 80mph uses up to 25% more fuel than 70mph
- Idling: Leaving your engine running whilst stationary wastes fuel unnecessarily
- Harsh braking: Frequent hard braking wastes the energy used to accelerate
Vehicle Condition
- Tyre pressure: Under-inflated tyres increase rolling resistance and reduce MPG by 3-5%
- Engine maintenance: Dirty air filters, old spark plugs, and low oil levels reduce efficiency
- Wheel alignment: Misaligned wheels increase drag and fuel consumption
- Excess weight: Every 50kg of extra weight reduces MPG by approximately 2%
Environmental Factors
- Weather conditions: Cold weather reduces MPG by 12-15% as engines take longer to reach optimal temperature
- Traffic conditions: Stop-start urban driving typically achieves 30-40% lower MPG than motorway driving
- Road gradient: Hills and inclines significantly increase fuel consumption
- Air conditioning: Using air conditioning can reduce MPG by 10-15% in urban driving
Improving Your Fuel Economy
Immediate Actions
- Remove unnecessary weight: Clear out your boot and remove roof racks when not needed
- Check tyre pressure weekly: Maintain manufacturer-recommended pressure levels
- Plan your journeys: Combine multiple short trips into one longer journey
- Use cruise control: Maintain steady speeds on motorways and dual carriageways
Driving Techniques
- Anticipate traffic flow: Look ahead and adjust speed gradually
- Use higher gears earlier: Change up before 2,500rpm for petrol and 2,000rpm for diesel
- Coast when safe: Lift off the accelerator early when approaching stops
- Avoid short journeys: Engines are least efficient when cold
Regular Maintenance
- Service your vehicle regularly: Follow manufacturer service schedules
- Use the correct oil grade: Modern low-friction oils improve efficiency
- Replace air filters: Clean filters improve engine performance
- Check wheel alignment annually: Proper alignment reduces drag
MPG vs L/100km Conversion
The UK traditionally uses MPG, whilst most of Europe uses litres per 100 kilometres (L/100km). Lower L/100km values indicate better efficiency, opposite to MPG where higher is better.
| MPG (Imperial) | L/100km | Efficiency Rating |
|---|---|---|
| 70 MPG | 4.0 L/100km | Excellent |
| 60 MPG | 4.7 L/100km | Very Good |
| 50 MPG | 5.6 L/100km | Good |
| 40 MPG | 7.1 L/100km | Average |
| 30 MPG | 9.4 L/100km | Below Average |
| 20 MPG | 14.1 L/100km | Poor |
Conversion Formulae:
L/100km = 282.481 ÷ MPG (Imperial)
MPG (Imperial) = 282.481 ÷ L/100km
L/100km = 282.481 ÷ MPG (Imperial)
MPG (Imperial) = 282.481 ÷ L/100km
Frequently Asked Questions
What is a good MPG for a car in the UK?
A good MPG depends on vehicle type. For modern petrol cars, 40-50 MPG is considered good, whilst diesel cars should achieve 50-60 MPG. Small city cars often exceed 55 MPG, whilst larger vehicles and SUVs typically achieve 30-40 MPG. Hybrid vehicles can reach 60-70 MPG or higher.
Why is my actual MPG lower than the manufacturer’s figure?
Manufacturers test vehicles under controlled laboratory conditions (WLTP tests) that don’t reflect real-world driving. Actual MPG varies with driving style, traffic conditions, weather, load, and vehicle maintenance. Expect real-world MPG to be 10-25% lower than official figures, particularly in urban driving.
How often should I calculate my vehicle’s MPG?
Calculate your MPG every 2-3 fill-ups to establish a baseline average. Once you know your typical MPG, monitor it monthly. Sudden changes of more than 10% may indicate mechanical issues such as faulty oxygen sensors, fuel injectors, or spark plugs that require attention.
Does driving at 60mph really save fuel compared to 70mph?
Yes, substantially. Fuel consumption increases exponentially with speed due to air resistance. At 70mph, you use approximately 9% more fuel than at 60mph, and at 80mph you use about 25% more than at 70mph. Motorway driving at 60-65mph maximises fuel efficiency for most vehicles.
Can I improve my diesel car’s MPG?
Yes, diesel vehicles respond well to efficient driving techniques. Key improvements include avoiding excessive idling, maintaining steady motorway speeds, using higher gears early (above 2,000rpm), and ensuring regular maintenance. Diesel engines perform most efficiently on longer journeys once fully warmed up.
What’s the difference between Imperial and US gallons?
Imperial gallons (used in the UK) contain 4.546 litres, whilst US gallons contain 3.785 litres. An Imperial gallon is approximately 20% larger. If comparing MPG figures internationally, always verify which measurement is used. A vehicle achieving 50 MPG (US) equals approximately 60 MPG (Imperial).
How does hybrid vehicle MPG compare to conventional engines?
Hybrid vehicles typically achieve 20-40% better MPG than equivalent conventional petrol engines, particularly in urban driving where regenerative braking recovers energy. City driving may see hybrids achieve 60-70 MPG, whilst motorway driving benefits decrease as regenerative braking opportunities reduce.
Will using premium fuel improve my MPG?
For most vehicles, premium fuel provides no MPG benefit despite higher cost. Only use premium fuel if your manufacturer specifically requires it (typically high-performance engines). Standard unleaded meets requirements for the vast majority of UK vehicles. Focus on driving technique and maintenance for genuine MPG improvements.
Real-World MPG Examples
Urban Driving Scenario
A Ford Fiesta 1.0L EcoBoost covers 180 miles in city driving, using 32 litres of petrol.
Calculation: 180 miles ÷ (32 litres ÷ 4.546) = 180 ÷ 7.04 = 25.6 MPG
This is typical for urban stop-start conditions.
This is typical for urban stop-start conditions.
Motorway Driving Scenario
The same vehicle covers 350 miles on motorways, using 28 litres of petrol.
Calculation: 350 miles ÷ (28 litres ÷ 4.546) = 350 ÷ 6.16 = 56.8 MPG
Motorway driving typically achieves 50-100% better MPG than urban driving.
Motorway driving typically achieves 50-100% better MPG than urban driving.
Combined Driving Scenario
Over one week, a Volkswagen Golf diesel covers 420 miles using 35 litres of diesel.
Calculation: 420 miles ÷ (35 litres ÷ 4.546) = 420 ÷ 7.70 = 54.5 MPG
Combined figures represent typical mixed urban and motorway driving.
Combined figures represent typical mixed urban and motorway driving.
Annual Fuel Cost Estimator
Calculate your approximate annual fuel expenditure based on your vehicle’s MPG and driving patterns.
Example Calculation:
Annual mileage: 10,000 miles
Vehicle MPG: 45 MPG
Fuel price: 145p per litre
Fuel needed: 10,000 ÷ 45 = 222.2 gallons = 1,010 litres
Annual cost: 1,010 × £1.45 = £1,464.50
Annual mileage: 10,000 miles
Vehicle MPG: 45 MPG
Fuel price: 145p per litre
Fuel needed: 10,000 ÷ 45 = 222.2 gallons = 1,010 litres
Annual cost: 1,010 × £1.45 = £1,464.50
| Annual Mileage | 40 MPG Cost | 50 MPG Cost | 60 MPG Cost |
|---|---|---|---|
| 5,000 miles | £827 | £662 | £552 |
| 10,000 miles | £1,654 | £1,323 | £1,103 |
| 15,000 miles | £2,481 | £1,985 | £1,654 |
| 20,000 miles | £3,308 | £2,646 | £2,205 |
Based on average UK fuel price of 145p per litre. A 10 MPG improvement saves approximately £330 annually per 10,000 miles driven.
Common Calculation Errors
Not Filling the Tank Completely
Stopping the fuel pump prematurely creates inaccurate baseline measurements. Always fill until the pump automatically stops, then add a small amount more carefully. Consistent filling technique is crucial for accurate MPG tracking.
Using US Gallons Instead of Imperial Gallons
This is the most common calculation error. UK vehicles use Imperial gallons (4.546 litres), not US gallons (3.785 litres). Using US gallons inflates your calculated MPG by approximately 20%, creating false expectations.
Insufficient Distance Between Fill-ups
Calculating MPG over very short distances (under 100 miles) produces unreliable results. Small variations in filling technique have disproportionate effects. Aim for at least 200-300 miles between calculations for accuracy.
Mixing Different Fuel Types
If you usually use premium fuel but occasionally use standard, MPG comparisons become invalid. Engine management systems adjust to fuel quality, affecting consumption. Maintain consistency for accurate tracking.
Ignoring Driving Condition Changes
Comparing summer motorway MPG to winter urban MPG creates meaningless results. Track MPG under similar conditions (same routes, weather, load) to identify genuine changes indicating mechanical issues.
References
Department for Transport (2024). Vehicle Emissions Testing Programme. GOV.UK. Available at: https://www.gov.uk/government/publications/vehicle-emissions-testing-programme
Society of Motor Manufacturers and Traders (2024). Vehicle Fuel Consumption Data. SMMT.co.uk. Available at: https://www.smmt.co.uk
RAC Foundation (2024). Fuel Economy and Efficient Driving Practices. RAC.co.uk. Available at: https://www.rac.co.uk/drive/advice/fuel-watch/
Energy Saving Trust (2024). Efficient Driving Guidance for UK Motorists. energysavingtrust.org.uk. Available at: https://energysavingtrust.org.uk/advice/driving/
AA (Automobile Association) (2024). Fuel Price Reports and Consumption Analysis. theaa.com. Available at: https://www.theaa.com/driving-advice/fuels-environment