Your car's fuel economy determines how far you can travel on each tank – and how much every journey costs. Here's everything you need to know about MPG, from understanding the numbers to improving your own efficiency.
What is MPG?
MPG stands for "miles per gallon" – the number of miles your car can travel on one gallon of fuel. A higher MPG means better fuel economy. In the UK, we use imperial gallons (4.55 litres), which differ from US gallons (3.79 litres), so don't compare directly with American figures.
What's a Good MPG?
This varies by vehicle type, but here's a general guide for petrol cars:
Official vs Real-World MPG
You've probably noticed your car never achieves the MPG claimed by the manufacturer. That's because official figures are measured in laboratory conditions using standardised tests (WLTP). Real-world driving is very different.
Expect to achieve 10-20% less than the official combined figure in everyday driving. Short urban trips might be 30% worse, while steady motorway driving might match or exceed the official figure.
How to Calculate Your Real MPG
Fill your tank completely, reset the trip counter, drive normally until nearly empty, then fill up again. Divide the miles driven by the litres added, then multiply by 4.546 to get your imperial MPG.
What Affects Your Fuel Economy?
Many factors influence how much fuel you use. Some you can control, others you can't:
Speed
Air Con
Roof Box
Low Tyres
Cold Weather
City Driving
How to Improve Your MPG
1. Drive Smoothly
Aggressive acceleration and harsh braking waste fuel. Accelerate gently, anticipate traffic, and coast to a stop where possible. Smooth driving can improve economy by 10-15%.
2. Maintain Momentum
It takes more fuel to get moving than to stay moving. Keep a steady speed where possible, and use cruise control on motorways. Avoid unnecessary stops.
3. Slow Down
Driving at 70mph uses about 9% more fuel than 60mph. At 80mph, it's 25% more. Unless you're in a real hurry, the fuel savings of driving more slowly usually outweigh the time cost.
4. Reduce Weight and Drag
Clear out your boot – every 50kg of extra weight reduces economy by about 2%. Remove roof boxes and bike racks when not in use. Close windows at speed.
5. Check Your Tyres
Under-inflated tyres increase rolling resistance. Check pressures monthly and keep them at the recommended level (or slightly above for motorway driving).
6. Service Your Car
A well-maintained engine runs more efficiently. Dirty air filters, old spark plugs, and degraded oil all reduce fuel economy. Keep up with servicing.
Track Your Progress
Record your MPG each time you fill up. You'll spot trends, notice if something's wrong, and motivate yourself to drive more efficiently. Many drivers improve by 5-10% just by paying attention.
Fuel Economy and Cost Per Mile
Here's how MPG translates to cost per mile at current fuel prices (143p/litre):
- 60 mpg = 10.8p per mile
- 50 mpg = 13.0p per mile
- 40 mpg = 16.2p per mile
- 30 mpg = 21.7p per mile
Improving from 35 to 45 mpg saves about 5p per mile – that's £500 per year for someone driving 10,000 miles.
The Bottom Line
Understanding your car's fuel economy is the first step to reducing your fuel costs. Track your real-world MPG, adopt fuel-efficient driving habits, and keep your car well-maintained.
And of course, always shop around for the best fuel prices using Fuelwise – because even the most efficient car costs more to run when you're paying over the odds.