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Fuel Cost Calculator
Sign up to favourite this calculatorEstimate what a journey costs in fuel from distance, fuel economy and pump price.
Your estimated fuel cost
Based on a 150.0 miles one-way (300.0 miles round trip) at 45.0 MPG (UK / Imperial) and £1.50 per litre, split 2 ways.
Estimated total fuel cost
Fuel needed
30.31 L≈ 6.67 UK galCost per mile
£0.15£0.09 per kmCost per person
£22.73MPG (UK / Imperial) uses the UK Imperial gallon — exactly 4.54609 litres. This is not the same as the US gallon.
Journey and cost breakdown
| Item | Value |
|---|---|
| Trip type | Round trip (distance doubled) |
| Distance entered | 150.0 miles |
| Distance used for this journey | 300.0 miles |
| Distance in the other unit | 482.8 km |
| Fuel economy (MPG UK / Imperial) | 45.0 MPG (UK / Imperial) |
| Fuel used | 30.31 litres |
| Fuel used (Imperial gallons) | 6.667 UK gal |
| Fuel price per litre | £1.50 per litre |
| Total estimated fuel cost | £45.46 |
| Cost per mile | £0.15 |
| Cost per km | £0.09 |
Passenger split
| Item | Value |
|---|---|
| Passengers sharing fuel | 2 |
| Total estimated fuel cost | £45.46 |
| Cost per person | £22.73 |
Equivalent fuel economy
| Unit | Value |
|---|---|
| Litres per 100 km | 6.28 |
| Kilometres per litre | 15.93 |
| MPG (UK / Imperial) | 45.0 |
| MPG (US) | 37.5 |
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Assumptions and limits
- An estimate from the numbers you entered, for guidance only. It is not financial, tax or medical advice.
- Calculator version 1, last updated 25 October 2026.
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How to use this calculator
- Choose your unit system — Metric (kilometres and litres), UK MPG (miles and the Imperial gallon) or US MPG (miles and the US gallon) — and your currency.
- Enter your journey distance, and choose one way or round trip.
- Enter the number of passengers sharing the fuel cost, if more than one.
- Enter your vehicle's fuel economy in the unit shown — L/100 km or km/L in Metric, MPG (UK / Imperial) in UK MPG, or MPG (US) in US MPG.
- Enter the pump price, in the price unit that matches your system.
- Read the estimated total fuel cost, fuel needed, cost per distance unit and, if you entered more than one passenger, the cost per person — plus the full journey breakdown below.
What do I need to enter?
- Unit system — Metric (km and litres), UK MPG (miles and the Imperial gallon) or US MPG (miles and the US gallon). It sets which economy and price units appear.
- Distance — one-way distance from 0 up to 20,000 km (about 12,400 miles).
- Trip type — One way, or Round trip, which doubles the distance.
- Passengers sharing fuel — a whole number from 1 to 100, used to split the cost.
- Fuel economy — litres per 100 km or km per litre in Metric, or MPG in the UK and US systems. It must be above 0, up to 100 in Metric or 1,000 in MPG.
- Fuel price — per litre, per Imperial gallon (UK MPG) or per US gallon (US MPG), from 0 up to 100 per litre or its gallon equivalent.
What do the results show?
- Estimated total fuel cost — the main figure for the whole journey, round trip included.
- Fuel needed — litres used, with the gallon equivalent in the UK and US systems.
- Cost per km or mile — total cost divided by distance, with the other unit beneath it.
- Cost per person — total cost divided by passengers, shown when more than one is entered; otherwise Journey distance appears instead.
- Breakdown tables — the journey and cost working, the passenger split, and your fuel economy in L/100 km, km/L, UK MPG and US MPG.
How is fuel cost calculated?
This calculator works out how much fuel a journey uses, then multiplies that by the fuel price. The fuel-used step depends on which fuel-economy unit you entered.
total cost = fuel used × price per litre
- L/100 km: fuel used (litres) = distance (km) × economy (L/100 km) ÷ 100
- km/L: fuel used (litres) = distance (km) ÷ economy (km/L)
- MPG (UK / Imperial): fuel used (litres) = (distance (miles) ÷ MPG) × 4.54609
- MPG (US): fuel used (litres) = (distance (miles) ÷ MPG) × 3.785411784
- a price entered per gallon is converted to price per litre before multiplying
For example, a 150-mile round trip is 300 miles. At 45 MPG (UK / Imperial), that uses 300 ÷ 45 = 6.667 Imperial gallons, which is 6.667 × 4.54609 ≈ 30.31 litres. At £1.50 per litre, the total cost is 30.31 × £1.50 ≈ £45.46 — £22.73 each if split between two people.
What is the difference between UK MPG and US MPG?
"MPG" means miles per gallon in both countries, but the gallon itself is a different size, so the same MPG number describes a different real fuel economy:
| Standard | Exact size |
|---|---|
| UK / Imperial gallon | 4.54609 litres |
| US liquid gallon | 3.785411784 litres |
Because the Imperial gallon holds more fuel, the same vehicle's economy is a higher number in MPG (UK / Imperial) than in MPG (US) — 45 MPG (UK / Imperial) is roughly 37.5 MPG (US), not 45. This calculator never carries an MPG figure from one standard to the other without converting it, and always labels which gallon a figure uses.
For a quick litres-to-gallons conversion on its own, without the fuel-cost maths, see the Litres to Gallons Converter.
How does the round-trip option work?
Choosing "Round trip" doubles the distance you entered before calculating fuel used and cost — round-trip distance = one-way distance × 2. Enter your one-way distance either way; there is no separate field for a return leg of a different length in this version of the calculator.
How is cost per mile or per kilometre calculated?
Cost per distance unit is the total estimated fuel cost divided by the total distance driven: cost per km = total cost ÷ distance in km, and cost per mile = total cost ÷ distance in miles. This calculator shows both, so a distance entered in one unit can still be compared against a cost figure quoted in the other.
What does this calculator assume, and what does it not do?
This calculator assumes a constant fuel economy, a constant distance and a single fuel price for the whole journey — it does not plan a route, look up live fuel prices, model tank size or refuelling stops, or account for traffic, speed, weather, terrain, load, driving style or idling. It does not calculate emissions, fuel or mileage tax, mileage reimbursement, or anything about an electric vehicle. It is an estimate from the figures you enter, not a prediction of what a specific journey will actually cost.
Frequently asked questions
How do I calculate the fuel cost of a trip?
Work out how much fuel the trip uses, then multiply by the price per litre (or per gallon): fuel used = distance ÷ economy (or distance × economy ÷ 100 for L/100 km), and cost = fuel used × price. This calculator does that arithmetic for Metric L/100 km or km/L, UK MPG (Imperial gallon) and US MPG (US gallon), and shows the working in the breakdown table below the results.
How does L/100 km fuel economy work?
L/100 km is the litres of fuel a vehicle uses to travel 100 kilometres, so a lower figure means better economy — a car using 6 L/100 km needs 6 litres for every 100 km driven. Fuel used for a journey is distance in km × L/100 km ÷ 100. It is the standard fuel-economy figure in most of Europe, alongside km/L, which is its reciprocal (100 ÷ L/100 km).
Is UK MPG the same as US MPG?
No — they use different gallons, so the same MPG number means a different real fuel economy. UK MPG (Imperial) is miles per Imperial gallon, exactly 4.54609 litres. US MPG is miles per US liquid gallon, exactly 3.785411784 litres, which is smaller — so for the same real economy, the US MPG figure is always a lower number than the UK MPG figure. This calculator keeps the two separate throughout and never treats one as the other.
How do I calculate the fuel cost of a round trip?
Double the one-way distance before working out fuel used and cost: round-trip distance = one-way distance × 2. Choose "Round trip" in this calculator and enter the one-way distance — it doubles the distance automatically before calculating fuel used and cost, so there is no separate return-distance field to fill in.
How do I split a fuel cost between passengers?
Divide the total estimated fuel cost by the number of people sharing it: cost per person = total fuel cost ÷ number of passengers. Enter the number of passengers sharing fuel — from 1 to 100 — and this calculator splits the total cost evenly and shows the per-person figure alongside the full breakdown.
Why might my actual fuel use and cost be different from this estimate?
This calculator assumes a constant fuel economy, distance and fuel price — real driving rarely holds all three constant. Traffic, speed, weather, terrain, vehicle load, driving style, idling, air conditioning, a different route, and a fuel price that changes between fill-ups can all move actual fuel use and cost away from this estimate.
Can I use this calculator for an electric vehicle?
No. This calculator works in litres, Imperial and US gallons and pump price per litre or gallon — it has no unit or input for electricity, kWh or a home or public charging rate, and it does not calculate charging cost, EV range or emissions.
Does this calculator use live fuel prices?
No. It only calculates from the pump price you type in — it does not look up, fetch or store today's fuel prices, and it does not know your location, route or the price at any particular station. Enter the price you have seen or expect to pay.
Last updated 25 October 2026.