What is good MPG for a car in the UK?

For petrol cars, 40-50 MPG is considered good, with 50+ MPG being excellent. For diesel cars, 50-60 MPG is good, with 60+ MPG being excellent. Modern hybrids can achieve 60-80 MPG. Real-world figures are typically 15-20% lower than manufacturer claims due to WLTP testing conditions.

How do I calculate my car's real MPG?

Fill your tank completely, reset your trip meter, drive normally until near empty, fill up again and note the litres used. Calculate: MPG = Miles driven ÷ Litres used × 4.546. For accuracy, average over 3-4 tanks covering different driving conditions.

Is petrol or diesel cheaper to run in the UK?

Diesel cars are typically 15-20% more fuel efficient but diesel costs about 5-10p more per litre. For high-mileage drivers (15,000+ miles per year), diesel is usually cheaper overall. For lower mileage or city driving, petrol is often more economical when factoring in higher diesel purchase prices and maintenance costs.

How can I improve my car's fuel economy?

Key improvements: maintain correct tyre pressure (adds up to 3% efficiency), remove roof boxes when not in use (saves up to 25% at motorway speeds), drive smoothly without harsh acceleration, use cruise control on motorways, turn off air conditioning when not needed (saves 5-10%), and keep speed at 60-65mph where safe (70mph uses 9% more fuel than 60mph).

Fuel Economy Calculator Guide - MPG to L/100km UK 2025

Knowing your car's actual fuel economy helps you budget accurately, spot mechanical problems early, and make informed decisions about driving habits. Real-world MPG often differs significantly from manufacturer claims—typically 15-20% lower under normal UK driving conditions.

UK vs US MPG: UK gallons are 4.546 litres while US gallons are only 3.785 litres. A car rated at 40 UK MPG would be approximately 33 US MPG. Always check which standard is being used when comparing figures.

How to Calculate Your Real MPG

The most accurate method is the "brim-to-brim" calculation over multiple fill-ups:

MPG Formula:
MPG = Miles driven ÷ Litres used × 4.546

Example: 300 miles on 40 litres = 300 ÷ 40 × 4.546 = 34.1 MPG

Fill your tank completely (to the first click)
Reset your trip meter to zero
Drive normally until nearly empty
Fill up again and note exactly how many litres went in
Note your trip meter reading
Apply the formula above

Pro Tip: Average your results over 3-4 fill-ups covering different conditions (motorway, city, mixed) for the most accurate picture of your typical fuel economy.

MPG to L/100km Conversion

European cars often display fuel consumption in litres per 100 kilometres. Lower L/100km means better economy (opposite to MPG where higher is better).

UK MPG	L/100km	Economy Rating
25	11.3	Poor
30	9.4	Below average
35	8.1	Average (older petrol)
40	7.1	Average (modern petrol)
45	6.3	Good
50	5.6	Very good
55	5.1	Excellent (diesel)
60	4.7	Excellent
70	4.0	Outstanding (hybrid)
80+	3.5 or less	Exceptional (PHEV)

Conversion Formulas

MPG to L/100km: 282.48 ÷ MPG = L/100km
L/100km to MPG: 282.48 ÷ L/100km = MPG

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Fuel Cost Per Mile

Understanding cost per mile helps compare vehicles and budget for journeys. Based on current UK fuel prices (January 2025):

MPG	Cost/Mile (Petrol 143p/L)	Cost/Mile (Diesel 152p/L)	100 Miles Cost
30 MPG	21.6p	22.9p	£21.60-£22.90
35 MPG	18.5p	19.6p	£18.50-£19.60
40 MPG	16.2p	17.2p	£16.20-£17.20
45 MPG	14.4p	15.3p	£14.40-£15.30
50 MPG	13.0p	13.8p	£13.00-£13.80
55 MPG	11.8p	12.5p	£11.80-£12.50
60 MPG	10.8p	11.5p	£10.80-£11.50

Annual Fuel Cost by Mileage

See how your annual fuel costs compare based on your MPG and yearly mileage (petrol at 143p/L):

Annual Miles	30 MPG	40 MPG	50 MPG	60 MPG
5,000	£1,080	£810	£650	£540
8,000	£1,728	£1,296	£1,040	£864
10,000	£2,160	£1,620	£1,300	£1,080
12,000	£2,592	£1,944	£1,560	£1,296
15,000	£3,240	£2,430	£1,950	£1,620
20,000	£4,320	£3,240	£2,600	£2,160

Fuel Price Impact: A 10p/litre price increase adds approximately £100-200 per year for an average driver (10,000 miles). A car achieving 50 MPG instead of 30 MPG saves over £1,000 annually at current prices.

Petrol vs Diesel Economics

Diesel cars typically achieve 15-20% better MPG but diesel costs more per litre. The break-even point depends on your annual mileage.

Factor	Petrol	Diesel
Fuel price (2025 avg)	~143p/litre	~152p/litre
Typical MPG (family car)	40-45 MPG	50-55 MPG
Purchase price	Lower	£1,000-2,000 more
Road tax (VED)	Usually lower	Usually higher
Maintenance costs	Lower	Higher (DPF, injectors)
Best for	Under 10,000 miles/year	15,000+ miles/year

Rule of Thumb: If you drive less than 12,000 miles per year, petrol is usually more economical overall. Above 15,000 miles, diesel often saves money despite higher fuel and maintenance costs.

Typical MPG by Vehicle Type

Real-world figures from UK drivers (expect 15-20% less than manufacturer WLTP claims):

Vehicle Type	Petrol MPG	Diesel MPG
City car (Fiat 500, VW Up)	45-55	55-65
Supermini (Ford Fiesta, VW Polo)	40-50	50-60
Hatchback (VW Golf, Ford Focus)	35-45	45-55
Family saloon (BMW 3 Series)	30-40	40-50
Estate car (VW Passat)	30-38	40-50
SUV/Crossover (Nissan Qashqai)	30-40	40-50
Large SUV (Range Rover)	20-28	30-38
Sports car	25-35	-
Hybrid (Toyota Prius)	55-70	-
PHEV (electric mode)	100+ (electric)	-

Speed and Fuel Economy

Driving speed has a significant impact on fuel consumption. Air resistance increases exponentially with speed.

Speed	Relative Fuel Use	Notes
50 mph	Baseline (100%)	Most efficient cruising speed
60 mph	+5%	Good balance of speed and economy
70 mph	+9%	UK motorway limit
80 mph	+25%	Illegal and expensive
90 mph	+40%	Very expensive, dangerous

Motorway Mathematics: Driving at 60mph instead of 70mph on a 100-mile journey takes just 8 minutes longer but saves approximately 10% on fuel—about £1.50 worth. Over a year of commuting, this adds up to significant savings.

How to Improve Fuel Economy

Vehicle Maintenance

Tyre pressure: Check monthly—underinflation by 10 PSI wastes 3% fuel
Air filter: Dirty filter can reduce economy by up to 10%
Engine oil: Use manufacturer-recommended grade
Wheel alignment: Misalignment causes drag and uneven wear
Spark plugs: Worn plugs reduce efficiency (petrol cars)

Driving Habits

Smooth acceleration: Gentle throttle uses less fuel
Anticipate traffic: Coast to red lights rather than late braking
Cruise control: Maintains steady speed on motorways
Engine off: Don't idle for more than 30 seconds
Higher gears: Shift up early—2,000-2,500 RPM is efficient

Vehicle Setup

Remove roof box: Saves up to 25% at motorway speeds
Remove roof bars: Saves up to 10%
Clear the boot: Every 50kg extra costs 2% economy
Air conditioning: Uses 5-10% extra fuel when running
Windows up at speed: Open windows create drag above 45mph

Combined Savings: Implementing all these tips can improve your real-world MPG by 15-25%, potentially saving £300-500 per year for an average driver.

Signs Your MPG Has Dropped

If your fuel economy suddenly worsens, investigate these common causes:

Dragging brakes: Feel for warm wheels after driving
Low tyre pressure: Check all four corners
Faulty oxygen sensor: Check engine light may illuminate
Clogged fuel injectors: Causes rough running
Thermostat stuck open: Engine runs cold
Wheel bearing issues: Listen for humming noise
Changed driving conditions: More traffic, hillier routes

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Fuel Economy in the UK: What Drivers Need to Know

Fuel costs represent one of the largest motoring expenses for UK drivers. With approximately 33 million cars registered in the UK, and petrol prices averaging 140-150 pence per litre in 2025, the average UK household spends over 1,200 pounds per year on fuel. The AA Fuel Price Report tracks regional variations, with fuel typically costing 3-5p per litre more at motorway service stations compared to supermarket forecourts. Supermarkets such as Asda, Tesco, Sainsbury's, and Morrisons consistently offer the lowest fuel prices in the UK.

UK fuel economy is measured in miles per gallon (mpg) using the imperial gallon (4.546 litres), which differs from the US gallon (3.785 litres). This means UK mpg figures are always higher than US mpg figures for the same vehicle. For comparison with European standards, many manufacturers now quote fuel consumption in litres per 100 kilometres. Under the WLTP (Worldwide Harmonised Light Vehicle Test Procedure) testing regime, introduced in 2017, official fuel economy figures have become more realistic than the older NEDC test, though real-world mpg typically still falls 10-15% short of official claims. The UK Government's Vehicle Excise Duty (road tax) is linked to CO2 emissions, giving drivers a financial incentive to choose more fuel-efficient vehicles.

Frequently Asked Questions About Fuel Economy

What is good fuel economy for a UK car?

For a modern petrol car in the UK, achieving 45-55 mpg in real-world driving is considered good, while 55-70 mpg is excellent. Diesel cars typically achieve 50-65 mpg in practice. Small city cars like the Toyota Yaris or Volkswagen Polo can exceed 55 mpg, while hybrid vehicles such as the Toyota Corolla Hybrid regularly achieve 60-70 mpg. Larger SUVs and performance cars may only manage 25-35 mpg. For comparison, fully electric vehicles consume no fuel but use approximately 3-4 miles per kWh of electricity, costing roughly 5-8 pence per mile compared to 12-16 pence per mile for a petrol car.

Why is my real-world mpg lower than the official figure?

Official fuel economy figures are measured under controlled laboratory conditions using the WLTP test cycle, which cannot fully replicate real-world driving conditions. Factors that reduce your actual mpg include cold weather (engines are less efficient when cold), aggressive driving style (rapid acceleration and heavy braking), heavy traffic and stop-start conditions, use of air conditioning or heating, under-inflated tyres, carrying heavy loads, and driving at motorway speeds above 60 mph. The Energy Saving Trust estimates that eco-driving techniques can improve real-world fuel economy by up to 15%, saving the average UK driver around 180 pounds per year.

How do I convert between UK mpg, US mpg, and litres per 100km?

To convert UK mpg to litres per 100km, divide 282.48 by the mpg figure. For example, 50 UK mpg equals 282.48 divided by 50 = 5.65 litres per 100km. To convert UK mpg to US mpg, multiply by 0.8327. So 50 UK mpg equals approximately 41.6 US mpg. These conversions are important when comparing vehicles tested in different markets or reading international car reviews. Many UK car manufacturers now provide fuel consumption figures in both mpg and L/100km, and most trip computers in modern vehicles allow you to switch between display units.

Does the UK ZEV mandate affect fuel economy standards for new cars?

Yes, the UK's Zero Emission Vehicle (ZEV) mandate, introduced in January 2024, requires that an increasing percentage of new car sales must be fully electric. By 2030, at least 80% of new cars sold must be zero-emission, rising to 100% by 2035. While the mandate primarily targets electric vehicle adoption, it indirectly improves overall fleet fuel economy because manufacturers must either sell more efficient vehicles or pay compliance fees. For buyers of remaining petrol and diesel cars, the mandate means manufacturers are focusing their combustion engine development on maximum efficiency to meet parallel CO2 targets. The Department for Transport publishes annual compliance reports showing manufacturer progress toward these targets on GOV.UK.

How does tyre pressure affect fuel economy in UK driving conditions?

Under-inflated tyres are one of the most common and easily fixable causes of poor fuel economy in the UK. According to the Energy Saving Trust, driving with tyres that are 15 psi below the recommended pressure can increase fuel consumption by approximately 6%. The correct tyre pressure for your vehicle is listed on a sticker inside the driver's door frame or in the owner's manual, and it varies depending on vehicle load. UK MOT testing checks tyre condition but not inflation pressure, so regular self-checks are essential. Check pressures at least monthly and before long motorway journeys when tyres are cold. Most UK petrol stations offer free or low-cost digital air machines. Properly inflated tyres also improve safety, handling, and tyre longevity.

What is the most fuel-efficient speed to drive on UK motorways?

Research by the Department for Transport shows that the most fuel-efficient speed for most cars on UK motorways is between 55 and 65 mph. Driving at 70 mph uses approximately 9% more fuel than driving at 60 mph, while driving at 80 mph uses roughly 25% more fuel than 60 mph. This is because aerodynamic drag increases exponentially with speed, meaning the engine must work significantly harder at higher speeds. The UK national speed limit on motorways is 70 mph, and smart motorways may impose variable limits of 40-60 mph during congestion. Cruise control can help maintain a steady, fuel-efficient speed on motorways. The RAC Foundation estimates that simply reducing your motorway cruising speed from 70 mph to 60 mph could save the average commuter over 200 pounds per year in fuel costs.

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James Mitchell, ACCA

Chartered Accountant & Former HMRC Advisor

James is a Chartered Certified Accountant (ACCA) specialising in UK personal taxation and financial planning. With over 12 years in practice and a background as a former HMRC compliance officer, he brings authoritative insight to complex tax topics.