What is MPG, and how to improve yours
MPG (miles per gallon) is the standard measure of fuel efficiency in the UK. The higher the number, the more miles you travel per unit of fuel, and the less you spend. But the official MPG figure on a car's spec sheet is almost never what drivers experience on the road. Understanding the gap, and how to close it, is the foundation of getting the most from your fuel budget.
What's good MPG, by vehicle type
"Good" MPG varies significantly by vehicle class. A compact city car returning 50 mpg is acceptable; the same figure in an SUV would be exceptional. A more useful comparison is how your car's real-world MPG compares to similar vehicles.
Official figures vs real-world results
Official MPG figures are measured under the WLTP (Worldwide Harmonised Light Vehicle Test Procedure) testing cycle, introduced in 2018 and more realistic than the older NEDC cycle it replaced. Even so, real-world driving typically delivers 10–20% less than the WLTP figure, because test conditions don't capture:
- Cold weather: petrol engines use significantly more fuel when cold. A 5°C morning can reduce real-world mpg by 8–10% compared to a warm day.
- Heavy urban traffic: the test cycle includes less stop-start driving than many real commutes.
- Higher motorway speeds: WLTP tests up to 131mph but weights higher speeds more optimistically than most drivers experience.
- Accessories: air conditioning, rear defogger, heated seats, all add load and aren't consistently factored into test conditions.
How to measure your real MPG accurately
The most accurate method: fill the tank completely, reset your trip odometer, drive normally until near empty, fill the tank completely again. Divide the miles driven by the number of litres used (multiplied by 4.546 to convert to gallons). This gives your true mpg over real driving conditions.
Your on-board computer's MPG readout is useful for trends but is notoriously optimistic. Studies have found it overstates economy by 5–15% on average. Don't take it at face value.
The fastest ways to improve your MPG
- Smooth driving style: the highest-impact change. Anticipate, coast, avoid hard acceleration. See our driving style guide.
- Higher gears at lower revs: shift up at 1,500–2,000 rpm. A car cruising at 50mph in 5th uses far less fuel than the same speed in 4th.
- Correct tyre pressure: a 10 PSI deficit costs ~3% fuel economy. Check monthly.
- Reduce load: remove roof boxes, clear the boot, don't run the tank overweight.
- Regular servicing: a clean air filter, fresh spark plugs, and correct engine oil all contribute to optimal combustion.
Divide 282 by your MPG figure to get L/100km. A car doing 45 mpg uses 282 ÷ 45 = 6.3 L/100km. This is the standard used across Europe and becoming more common in UK car specs.