Miles Per Gallon Calculator

Calculate your car's fuel economy in MPG, L/100km and km/L from distance and fuel used.

Source: HMRC – Advisory fuel rates

Konstantin Iakovlev

By Konstantin Iakovlev · Founder, Calks.uk

Last updated: · Verified against HMRC and GOV.UK 2026/27 rates

Typical MPG by vehicle type:

Small car: 45-60 MPG | Family car: 35-50 MPG | SUV: 25-40 MPG | Van: 25-35 MPG

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Miles Per Gallon (MPG) measures how far your car travels on one UK gallon of fuel (4.546 litres). Higher MPG means lower running costs. To get accurate real-world MPG: fill to the brim, reset the trip counter, drive normally, then fill up again and note the litres added and distance covered.

Official WLTP manufacturer figures typically exceed real-world MPG by 10–25%. This calculator uses your actual journey data for a true fuel economy figure. It also converts to L/100km (European standard) and km/L.

HMRC's approved mileage rate for business travel is 45p per mile for the first 10,000 business miles and 25p thereafter (cars). Knowing your real MPG lets you calculate your true cost per mile and check whether this exceeds or falls short of the HMRC allowance.

UK MPG calculation — Imperial vs US. 1 UK gallon = 4.546 litres ≠ 1 US gallon = 3.785 litres. UK MPG higher than US MPG for same car. Convert: UK MPG × 0.833 = US MPG; US MPG × 1.201 = UK MPG. Sample: Toyota Prius 64 MPG UK = 53 MPG US. Calculation: distance (miles) ÷ fuel used (UK gallons) = MPG.

Typical UK MPG by car type 2026. Small petrol (Fiesta, Polo): 50-65 MPG combined. Family petrol (Focus, Golf): 40-55. SUV petrol (Qashqai, Sportage): 35-45. Diesel family: 50-65. Hybrid (Prius, Yaris): 60-80. Plug-in hybrid: 100+ with battery, declines after 30-50 miles. EV equivalent: 4-5 miles/kWh ≈ 120-150 MPGe. Sports car (M3, RS6): 25-35.

How to maximise MPG. Steady 50-60 mph most efficient (drop 10-20% above 70). Smooth acceleration: aggressive driving costs 30-40% fuel. Tyre pressure under-inflated 0.5 bar = 5-10% MPG loss. Roof racks: 10-25% loss on motorway. Cold engine first 5 miles: 10-15% waste. AC: 5-10% penalty. Cruise control: 5-10% saving.

WLTP vs real-world. UK new car MPG quoted under WLTP (since 2017). Real-world typically 80-90% of WLTP. '60 MPG WLTP' actually 50-54 MPG real driving. Sites for accurate figures: What Car? True MPG, Honest John Real MPG, Autocar. EV range: WLTP also 10-20% optimistic for winter (cold reduces 20-30%).

Total cost per mile. Petrol 45 MPG, £1.45/litre = 14.7p/mile fuel. EV home off-peak (8p/kWh): 2p/mile. EV public rapid (60-80p/kWh): 15-20p/mile. HMRC AMAP 45p/mile covers fuel + maintenance + insurance + tax for business mileage first 10,000 miles. Annual UK driver 8,000 miles: 45 MPG petrol = £1,300 fuel; EV home charging = £150-£300.

Example: 350-mile trip using 40 litres of fuel

  1. 40 litres ÷ 4.546 = 8.80 UK gallons
  2. MPG = 350 ÷ 8.80 = 39.8 MPG real-world
  3. Fuel cost at £1.40/litre: (40 × £1.40) ÷ 350 = 16.0p per mile
  4. HMRC rate is 45p/mile — covers fuel plus wear and depreciation

Source: HMRC – Advisory fuel rates

Frequently Asked Questions

How is MPG calculated?
MPG = miles travelled ÷ gallons used. To work it out: fill the tank, reset the trip meter, drive normally, refill when low, divide trip miles by litres × 0.22 (to convert litres to UK gallons). UK gallon = 4.546 litres (different from US gallon at 3.785 litres). Modern cars display MPG on the dashboard but onboard computers are often optimistic by 5-15% — manual calculation gives true real-world figures.
WLTP vs real-world MPG.
Manufacturer's quoted MPG (WLTP since 2017 — Worldwide Harmonised Light Vehicle Test Procedure) is the regulatory test cycle figure. Real-world driving typically achieves 75-85% of WLTP. A car quoted at 50 mpg WLTP realistically delivers 38-43 mpg in mixed driving. The old NEDC test (pre-2017) was even more optimistic — cars from 2010-2017 often undershoot quoted figures by 25-30%.
MPG vs miles per pound — what really matters.
MPG alone misleads: a 50 mpg diesel at £1.50/litre = 13.6p/mile. A 40 mpg petrol at £1.45/litre = 16.5p/mile. Diesel wins per mile despite same MPG appearing. An EV at 4 miles/kWh on home tariff (8p/kWh) = 2p/mile. Compare miles-per-pound rather than MPG. UK average annual mileage 7,400 miles: 16.5p/mile = £1,221/year fuel; 2p/mile = £148/year fuel. £1,000+/year saving on running cost alone.