MPG Calculator
Calculate journey costs, fuel consumption, and your real-world MPG. Plan your trips and understand exactly what your car costs to run.
Calculate how much a journey will cost in fuel based on distance, your car's MPG, and current fuel prices.
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Understanding MPG
MPG (Miles Per Gallon) measures how far your car can travel on one gallon of fuel. A higher MPG means better fuel economy and lower running costs.
In the UK, we use imperial gallons (4.546 litres), which differs from US gallons (3.785 litres). UK MPG figures are around 20% higher than US MPG for the same vehicle.
Tip: Manufacturer MPG figures are measured under test conditions and typically run 15-20% higher than real-world driving. Use our Real MPG calculator to find your actual fuel economy.
Factors Affecting Fuel Economy
Several factors can significantly affect your car's fuel economy:
Driving Style
Aggressive acceleration and braking can reduce fuel economy by up to 33%. Smooth, steady driving is far more efficient.
Tyre Pressure
Under-inflated tyres increase rolling resistance. Keeping tyres at the correct pressure can improve MPG by up to 3%.
Vehicle Weight
Every extra 50kg reduces fuel economy by around 1-2%. Remove unnecessary items from your boot to save fuel.
Air Conditioning
Running the AC can reduce fuel economy by 5-10%. At lower speeds, opening windows is more efficient.
Journey Type
Motorway driving at steady speeds is typically more fuel-efficient than stop-start city driving.
MPG vs L/100km
While the UK traditionally uses MPG, European cars often display fuel consumption in L/100km (litres per 100 kilometres). Here's how they compare:
Common MPG to L/100km Conversions
| MPG (UK) | L/100km | Efficiency |
|---|---|---|
| 70 | 4.0 | Excellent |
| 60 | 4.7 | Very Good |
| 50 | 5.7 | Good |
| 45 | 6.3 | Good |
| 40 | 7.1 | Average |
| 35 | 8.1 | Average |
| 30 | 9.4 | Below Average |
| 25 | 11.3 | Poor |
| 20 | 14.1 | Poor |
Note: Lower L/100km = better fuel economy. Higher MPG = better fuel economy.
Top 10 Tips for Better Fuel Economy
These tried-and-tested tips can make a real difference to your fuel economy. Start saving straight away.
Drive Smoothly
Aggressive accelerating and braking wastes up to 60% more fuel. When pulling away from lights, accelerate gently and smoothly.
Read the Road Ahead
Look ahead for traffic lights, parked cars, or anything that might require you to slow down. By anticipating what's coming, you can ease off early and avoid stopping completely.
Don't Rev the Engine
Revving the engine whilst stationary does nothing except waste fuel. Avoid unnecessary revving at traffic lights or when parked.
Use Gears Sensibly
Correct use of gears can save up to 15% on fuel. Change up into a higher gear as soon as it's safe and practical to do so.
Stick to the Speed Limit
Driving at 80mph uses 10-20% more fuel than 70mph. For a 20-mile motorway journey, 80mph saves only around 2 minutes compared to 70mph. Driving at 50mph uses 20-30% less fuel than 70mph.
Check Your Tyres
Check tyre pressures at least every fortnight. Under-inflated tyres increase fuel consumption by 3% and wear out faster. Check your owner's manual for the correct pressures.
Don't "Warm Up" the Engine
On cold mornings, don't leave your car idling to warm up. It causes unnecessary engine wear and wastes fuel. Use de-icer and drive off as soon as you can see clearly.
Avoid Short Trips
A cold engine uses twice as much fuel as a warm one. Consider walking for very short journeys - the exercise will do you good!
Use Air Conditioning Wisely
Only use AC when you really need it. At low speeds, use the blowers instead. Avoid opening windows at high speed as this increases drag and wastes more fuel than AC.
Keep Your Car Well Maintained
Follow the recommended service schedule. A well-tuned engine with fresh oil and clean air filters runs more efficiently than a neglected one.
Alternative Fuels
There are several alternatives to petrol and diesel. Some require modifications to your vehicle, whilst others are only available when buying a new car. Here are some of the most viable options available today.
Hybrid Cars
Petrol + Electric
Hybrid cars are one of the most well-known alternative fuel options, with the Toyota Prius being the most familiar example. They combine a small petrol engine with an electric motor and battery system.
The on-board computer decides when to use the engine, electric motor, or a combination of both for optimal efficiency. For example, a hybrid may use the efficient electric motor to pull away, then switch to the engine when more power is needed.
Best for: Stop-start city driving where hybrids excel. For motorway driving, modern diesel superminis may offer similar economy at a lower purchase price.
Electric Vehicles (EVs)
100% Electric
Fully electric vehicles run entirely on battery power with zero tailpipe emissions. The UK's charging network has expanded significantly, with over 50,000 public charging points now available.
Running costs are typically much lower than petrol or diesel - charging at home overnight can cost as little as 2-3p per mile compared to 10-15p for a conventional car.
Best for: Daily commutes and urban driving. Modern EVs offer 200-300+ miles of range, making them practical for most journeys.
Biodiesel
Plant-based Diesel
Biodiesel is produced from plant sources such as rapeseed oil rather than crude oil. It's perfectly legal in the UK and can be used in most modern diesels without any modifications.
It can be mixed with regular diesel in any ratio. However, biodiesel has been known to damage natural rubber in fuel lines on older (pre-1995) vehicles, so check compatibility first.
Key benefit: Biodiesel is carbon-neutral and can even be made at home from waste oils (though you'll still pay fuel duty of around 27p per litre).
LPG (Autogas)
Liquefied Petroleum Gas
LPG (Liquefied Petroleum Gas), also known as Autogas, is a mixture of propane and butane. It's the most widely available alternative fuel in the UK with over 1,400 filling stations.
Most petrol cars can be converted to run on LPG for around £1,500-2,500. LPG typically costs around half the price of petrol, though fuel economy is about 15-20% lower.
Best for: High-mileage drivers who can recoup the conversion cost. LPG also produces fewer emissions than petrol.
Best Cars for MPG
Looking for the most fuel-efficient car? Here's a breakdown of the best performers across different fuel types. Bear in mind that official figures are tested under laboratory conditions - real-world economy is typically 10-20% lower.
Average Fuel Economy of UK Cars
Urban
35-40
MPG
Extra Urban
50-60
MPG
Combined
45-50
MPG
Most Fuel-Efficient Cars (Non-Electric)
| Make & Model | Fuel Type | Combined MPG |
|---|---|---|
| Toyota Yaris Hybrid | Hybrid | 68.9 |
| Hyundai Ioniq Hybrid | Hybrid | 62.8 |
| Suzuki Swift 1.2 Hybrid | Mild Hybrid | 57.6 |
| Peugeot 208 1.5 BlueHDi | Diesel | 56.5 |
| Renault Clio 1.5 dCi | Diesel | 55.4 |
| Toyota Corolla Hybrid | Hybrid | 54.3 |
| Honda Jazz Hybrid | Hybrid | 53.3 |
| Fiat 500 1.0 Hybrid | Mild Hybrid | 52.3 |
Most Fuel-Efficient Petrol Cars (Non-Hybrid)
| Make & Model | Engine | Combined MPG |
|---|---|---|
| Toyota Aygo X | 1.0-litre 3-cylinder | 53.3 |
| Citroen C1 | 1.0-litre VTi | 52.3 |
| Peugeot 108 | 1.0-litre VTi | 52.3 |
| Kia Picanto | 1.0-litre MPI | 50.4 |
| Hyundai i10 | 1.0-litre MPI | 50.4 |
| Volkswagen Up! | 1.0-litre TSI | 49.6 |
| Suzuki Ignis | 1.2-litre Dualjet | 48.7 |
| Dacia Sandero | 1.0-litre TCe | 47.9 |
Key Takeaways
- Hybrid superminis dominate the efficiency charts, with the Toyota Yaris Hybrid leading the pack
- Small diesel engines still offer excellent economy, particularly for higher-mileage drivers
- For pure petrol, city cars with 1.0-litre engines offer the best fuel economy
- Real-world MPG is typically 10-20% lower than official WLTP figures
Frequently Asked Questions
What is a good MPG for a car in the UK?
A good MPG in the UK is typically 50-60 MPG for a diesel or hybrid, and 40-50 MPG for a petrol car. The average UK car achieves around 45-50 MPG combined. Hybrids like the Toyota Yaris Hybrid can achieve nearly 70 MPG, while older or larger vehicles may only manage 25-35 MPG.
How do I calculate my car's real MPG?
To calculate real MPG: 1) Fill your tank completely and note the mileage. 2) Drive normally until you need to refuel. 3) Fill up again and note how many litres you added. 4) Calculate: (Miles driven ÷ Litres used) × 4.546 = MPG. Our Real MPG calculator above does this automatically - just enter your fuel spend, price per litre, and miles driven.
Why is my real MPG lower than the manufacturer's figure?
Manufacturer MPG figures are tested under ideal laboratory conditions (WLTP test). Real-world driving typically achieves 10-20% less due to: traffic conditions, driving style, air conditioning use, cold weather, roof boxes, under-inflated tyres, and carrying heavy loads. City driving especially reduces MPG compared to test conditions.
What is the difference between UK MPG and US MPG?
UK MPG uses imperial gallons (4.546 litres), while US MPG uses US gallons (3.785 litres). This means UK MPG figures are about 20% higher than US figures for the same fuel consumption. For example, 40 MPG (UK) equals approximately 33 MPG (US). Always check which measurement is being used when comparing vehicles.
How do I convert MPG to L/100km?
To convert UK MPG to L/100km, divide 282.48 by the MPG figure. For example: 40 MPG = 282.48 ÷ 40 = 7.06 L/100km. To convert L/100km to UK MPG, divide 282.48 by the L/100km figure. Use our Convert Units tab above for instant conversions.
How much does it cost to drive 100 miles?
At average UK fuel prices (around 140p per litre) and average fuel economy (45 MPG): 100 miles costs approximately £14. A very efficient car at 60 MPG would cost around £10.50, while a less efficient car at 30 MPG would cost around £21. Use our Journey Cost calculator for exact figures.
Does driving slower save fuel?
Yes. Driving at 50mph uses 20-30% less fuel than 70mph. Driving at 70mph uses about 9% less fuel than 80mph. The most fuel-efficient speed is around 45-50mph in top gear. However, the biggest savings come from smooth acceleration and anticipating traffic to avoid unnecessary braking.
Does air conditioning affect fuel consumption?
Yes, air conditioning typically reduces fuel economy by 5-10%. At low speeds (under 40mph), opening windows is more efficient. At higher speeds (over 50mph), the drag from open windows uses more fuel than the AC. Use AC sparingly and set it to a moderate temperature.
How much fuel does idling use?
A typical car uses 0.5-1 litre of fuel per hour when idling, depending on engine size. This equates to roughly 1-2p per minute. If you're stopped for more than 30-60 seconds (except in traffic), turning off the engine saves fuel. Many modern cars have automatic stop-start systems for this reason.
Is diesel more fuel efficient than petrol?
Diesel engines are typically 15-20% more fuel efficient than petrol engines of equivalent power. However, diesel costs more per litre and diesel cars have higher purchase prices. Diesel is most cost-effective for high-mileage drivers (over 12,000 miles per year), particularly those doing motorway driving.
Check Your Vehicle's Full Details
Get your car's official MPG figures, emissions data, tax band, and more with our free vehicle check.