Why is my real MPG lower than the official figure?

Official WLTP figures are tested under controlled conditions. Real-world factors like cold weather, city driving, AC usage, and under-inflated tyres all reduce fuel economy. Most drivers achieve 10-25% less than the official figure.

How much does city driving affect fuel economy?

City driving can reduce fuel economy by 20-30% compared to the official figure. Frequent stopping and starting, idling in traffic, and low-speed driving are all inefficient. Start-stop systems help but cannot fully offset this.

Does AC really use that much fuel?

Yes, AC typically increases fuel consumption by 5-10%. At lower speeds the effect is proportionally greater. Above 50 mph, AC is actually more efficient than opening windows (which increases drag).

How does cold weather affect fuel economy?

Cold weather can reduce fuel economy by 10-20%. Cold engines run less efficiently, the heater uses energy, cold tyres have higher rolling resistance, and winter fuel blends can be less efficient. Short trips in cold weather are especially inefficient.

Does tyre pressure really matter?

Yes, under-inflated tyres increase rolling resistance significantly. Tyres at 80% of recommended pressure can reduce fuel economy by 3-5%. Severely under-inflated tyres also wear faster and are less safe.

CarCalcs

Fuel Economy by Conditions Calculator

See how driving conditions affect your real-world fuel economy.

Manufacturer MPG

Official WLTP combined figure

Driving Type

Driving type

Temperature

Temperature in °C

Tyre Pressure

Tyre specification from sidewall markings

Fuel Price

Current price of fuel

Annual Mileage

Total miles driven per year

Air conditioning on

Adds extra fuel consumption

Roof rack / box fitted

Increases aerodynamic drag

How We Calculate This

This calculator applies real-world adjustment factors to your official MPG figure based on your driving conditions.

Adjustment Factors

City driving: -25% (default), motorway: -5%, mixed: -12%
Cold weather: -0.5% per degree below 20°C
AC usage: -8% (default)
Roof load: -10% (default)
Low tyre pressure: -3% slight, -8% significant

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Actual figures may vary based on driving conditions, vehicle specifications, and other factors.