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Fuel Cost Calculator

Estimate what a journey costs in fuel from distance, fuel economy and pump price.

Choose your units

Unit system

Distance in miles, economy in MPG (UK / Imperial), price per litre or per Imperial gallon. UK MPG uses the Imperial gallon.

Changes formatting only, not the calculation.

Your journey

miles

Enter your planned driving distance.

Trip type

A round trip doubles the distance entered above.

The fuel cost is split equally between this many people.

Your fuel economy

MPG (UK)

Enter your vehicle's fuel economy in MPG (UK / Imperial). UK MPG uses the Imperial gallon — 4.54609 litres.

Your fuel price

£per litre

Enter the price shown at the pump.

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
£45.46
Fuel needed
30.31 L≈ 6.67 UK gal
Cost per mile
£0.15£0.09 per km
Cost per person
£22.73

MPG (UK / Imperial) uses the UK Imperial gallon — exactly 4.54609 litres. This is not the same as the US gallon.

Journey and cost breakdown

Journey distance, fuel economy, fuel used and cost breakdown
ItemValue
Trip typeRound trip (distance doubled)
Distance entered150.0 miles
Distance used for this journey300.0 miles
Distance in the other unit482.8 km
Fuel economy (MPG UK / Imperial)45.0 MPG (UK / Imperial)
Fuel used30.31 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

Fuel cost split equally between passengers
ItemValue
Passengers sharing fuel2
Total estimated fuel cost£45.46
Cost per person£22.73

Equivalent fuel economy

The fuel economy entered, shown in every common unit
UnitValue
Litres per 100 km6.28
Kilometres per litre15.93
MPG (UK / Imperial)45.0
MPG (US)37.5

How to use this calculator

  1. 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.
  2. Enter your journey distance, and choose one way or round trip.
  3. Enter the number of passengers sharing the fuel cost, if more than one.
  4. 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.
  5. Enter the pump price, in the price unit that matches your system.
  6. 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.

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:

UK Imperial gallon compared with the US liquid gallon
StandardExact size
UK / Imperial gallon4.54609 litres
US liquid gallon3.785411784 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.

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.