Fuel Cost Calculator — Trip Cost by Distance, Efficiency & Price
Distance, your car's consumption and the pump price → fuel needed, total cost and cost per person.
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Work out what a trip will cost in fuel. Enter the distance, your vehicle's fuel efficiency in whatever unit you know it — L/100 km, km/L, US mpg or UK mpg — and the price per litre or gallon, and get the litres or gallons you'll burn, the total cost, the cost per kilometre or mile, and the share per passenger.
Mixed units are the whole point: a British mpg figure with a euro-per-litre price on a French road trip comes out right.
How to use Fuel Cost Calculator
- Enter the distance in km or miles and tick "round trip" if you're coming back.
- Enter fuel efficiency in the unit your car reports — the tool converts.
- Enter the fuel price per litre or per US/UK gallon.
- Split between passengers to see what each person should chip in.
The gallon problem
A US gallon is 3.785 litres; a UK (imperial) gallon is 4.546 litres — 20% bigger. So a car rated 40 mpg in the UK does only about 33 mpg on the US measure, and "mpg" without a country is ambiguous. The efficiency and price dropdowns are separate precisely so you can pair a UK mpg with a US per-gallon price if that's the trip you're taking.
L/100 km versus mpg
They're inverses: lower L/100 km is better, higher mpg is better. 5 L/100 km ≈ 47 US mpg ≈ 56 UK mpg; 10 L/100 km ≈ 24 US mpg. The "same as" tile shows your figure in the other system as a sanity check — if it looks absurd, the wrong unit was picked.
Real-world consumption
Manufacturer figures are optimistic. Expect 10–20% worse in practice, more in winter, with a roof box, in stop-start traffic, or at high motorway speeds (drag grows with the square of speed — 130 km/h uses roughly 25% more fuel than 100 km/h). For a budget, use the number your car's trip computer actually shows over a full tank, or pad the sticker figure by 15%.
Splitting fairly
Fuel is only part of the cost of driving — tyres, servicing and depreciation typically double it. If you're sharing a long trip, splitting fuel alone is the friendly minimum; national mileage rates (like the IRS or HMRC per-mile allowances) are a fairer all-in figure. Round the per-person amount up; nobody has ever complained about paying a dollar less.
To compare cars or convert efficiencies in bulk, the unit converter handles mpg and L/100 km directly.
Frequently asked questions
Which mpg should I pick — US or UK?
Whichever country's figure you have. UK/imperial mpg numbers are about 20% higher than US mpg for the same car because the imperial gallon is 4.546 L against 3.785 L. Car reviews and dashboards in Britain use UK mpg; American ones use US mpg; everyone else uses L/100 km or km/L.
How do I find my car's fuel efficiency?
Best: fill the tank, reset the odometer, drive normally, refill and divide litres by distance (× 100 for L/100 km). Good: the trip computer's long-term average. Rough: the manufacturer's combined figure plus 10–15%, since official tests are optimistic.
Does the calculator include tolls, parking or wear?
No — fuel only. Tolls and parking vary too much to estimate, and wear-and-tear (tyres, servicing, depreciation) roughly doubles the per-mile cost of driving. For a fair split with passengers on a long trip, consider a per-mile allowance rate instead of fuel alone.
Why is my real cost higher than this?
Speed, load, climate control, cold engines and traffic all raise consumption above the rated figure — often 15–25% on a motorway trip with a full car. Enter the consumption your car actually shows rather than the brochure number, and the estimate will be close.
Can I use this for electric cars?
Not directly — the units are litres and gallons. The arithmetic is the same though: distance × kWh/100 km ÷ 100 × price per kWh. A typical EV uses 15–20 kWh/100 km.