Fuel Cost Calculator
Estimate what a drive costs in gas or electricity, split it between passengers, and work out real MPG or L/100 km from a fill-up. US and UK gallons handled.
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About this toolWhat is the Fuel Cost Calculator?
How much will the drive cost? Enter the distance, your car's fuel economy and the price at the pump, and the Fuel Cost Calculator shows the fuel needed and the bill for the trip, one way or there and back, plus each person's share if you are splitting it with friends. A 250 mile run in a 30 MPG car with gas at $3.40 a gallon comes to 8.33 gallons and $28.33.
It speaks every common unit. Economy can be miles per US gallon, miles per UK (imperial) gallon, litres per 100 km or km per litre, and switching units converts the figure for you. Prices can be per US gallon, per UK gallon or per litre, in eight currencies. A second mode turns a fill-up (miles driven and fuel added) into your real fuel economy, and a third mode prices an electric car trip from kWh per 100 km or miles per kWh and your electricity rate.
A small table also shows the cost if your mileage is 10% or 20% better or worse than you expect, because highway speed, a loaded car and cold weather move real-world economy more than most people assume.
- MPG (US and UK), L/100 km and km/L with automatic conversion
- Price per US gallon, UK gallon or litre in eight currencies
- Round trip and passenger cost splitting
- Fill-up mode that calculates your real fuel economy
- Electric vehicle mode with charging loss and MPGe
- Sensitivity table for better or worse mileage
- Shareable link, copy-ready summary, runs entirely in your browser
How to use the Fuel Cost Calculator
- Pick a mode: Trip fuel cost, Fuel economy from a fill-up, or Electric vehicle.
- Enter the one-way distance and choose miles or kilometres. Turn on Round trip to double it.
- Enter your fuel economy and its unit (or kWh/100 km, mi/kWh and similar for an EV). Changing the unit converts the number already in the box.
- Enter the fuel price and say whether it is per US gallon, per UK gallon or per litre, then choose your currency.
- Set how many people are sharing the cost and read the total, the share per person, the fuel needed and the cost per mile and per km.
Worked examples
A weekend road trip in the US
Input
250 miles one way, 30 MPG (US), $3.40 per gallon
Output
8.33 gallons, $28.33, or $0.113 per mile
250 / 30 = 8.33 gallons, and 8.33 x 3.40 = 28.33. Ticking Round trip doubles both to 16.67 gallons and $56.67.
Splitting a European drive three ways
Input
420 km each way, 6.8 L/100 km, 1.75 per litre, round trip, 3 people
Output
57.12 L, 99.96 total, 33.32 each
840 km x 6.8 / 100 = 57.12 litres. At 1.75 a litre that is 99.96, split three ways. The 6.8 L/100 km car is about 34.6 MPG in US terms.
Checking real mileage after a fill-up
Input
350 miles on the trip meter, 11.2 US gallons to refill
Output
31.25 MPG (US), 37.5 MPG (UK), 7.53 L/100 km
Fill to the first click, reset the trip meter, drive, then fill again. Distance / fuel is your real economy, which you can feed back into the trip mode.
The same trip in an electric car
Input
250 miles, 3.5 mi/kWh, $0.17 per kWh, 10% charging loss
Output
79.4 kWh from the grid, $13.49, 118 MPGe
250 / 3.5 = 71.4 kWh into the battery, divided by 0.9 for charging losses. Fast chargers often cost $0.40 to $0.60 per kWh, which would more than double the bill.
Background and insight
The arithmetic is simple once everything is in one unit: fuel = distance x consumption, and cost = fuel x price. The calculator converts internally to litres and kilometres using exact definitions: 1 mile is 1.609344 km, 1 US gallon is 3.785411784 litres (231 cubic inches) and 1 imperial gallon is 4.54609 litres. Because the imperial gallon is about 20% larger, the same car that does 30 MPG in the US is quoted as 36 MPG in the UK. Mixing the two is the most common reason online figures disagree.
L/100 km runs the other way from MPG: lower is better, and the two are reciprocals. To convert, divide 235.215 by MPG (US) or 282.481 by MPG (UK). Reciprocal units also mean savings are not linear. Going from 15 to 20 MPG saves far more fuel over 10,000 miles (167 gallons) than going from 40 to 50 MPG (50 gallons), which is why L/100 km is the better unit for comparing running costs.
For electric cars the calculator uses kWh drawn from the grid. Charging is not lossless, so a charging-loss field (10% by default) scales the battery energy up to what your meter records. It also reports MPGe using the US EPA equivalence of 33.705 kWh per gallon of gasoline, the figure printed on US window stickers.
Common use cases
Road trip budgeting
Price the fuel for a holiday drive before you leave and compare it with train or plane fares.
Sharing a ride fairly
Split the fuel bill between carpoolers or friends with the per-person figure, round trip included.
Choosing between two cars
Run the same trip with each car's MPG to see what the difference is worth per year.
Gas versus electric
Compare a petrol car's trip cost with an EV's at home and public charging rates.
Tracking real fuel economy
Turn fill-up receipts into MPG or L/100 km and spot a car that is starting to drink more.
Tips and limitations
- Make sure the MPG and the price use the same kind of gallon. A UK MPG figure with a US gallon price will be about 20% off.
- Official ratings (EPA in the US, WLTP in Europe) are measured on lab cycles. Real highway driving at 75 mph or more often comes in 10 to 20% worse.
- For an EV, enter the price you will really pay. Home off-peak rates and motorway fast chargers can differ by a factor of three or four.
- Average fuel economy over several tanks; one tank is affected by how full the pump left it.
- Fuel is only part of the cost of driving. Tolls, parking, tyres, servicing and depreciation are not included here.
Frequently asked questions
How do I calculate the fuel cost of a trip?
Divide the distance by your fuel economy to get the fuel needed, then multiply by the price per gallon or litre. For 300 miles at 30 MPG and $3.50 a gallon: 300 / 30 = 10 gallons, and 10 x 3.50 = $35. With L/100 km, multiply the distance in km by the L/100 km figure and divide by 100 to get litres.
Why is UK MPG higher than US MPG for the same car?
A UK imperial gallon is 4.546 litres and a US gallon is 3.785 litres, so a UK gallon takes you about 20% further. Multiply US MPG by 1.201 to get UK MPG. The calculator keeps the two separate and converts between them.
How do I convert MPG to L/100 km?
Divide 235.215 by miles per US gallon, or 282.481 by miles per UK gallon. 30 MPG (US) is 7.84 L/100 km and 50 MPG (UK) is 5.65 L/100 km. Choosing a different unit in the calculator does this conversion for you.
How do I work out my real MPG?
Fill the tank until the pump clicks off and reset the trip meter. Drive normally, then fill up again the same way. Divide the miles on the trip meter by the gallons you just added. Use the Fuel economy from a fill-up mode, and average a few tanks for a steadier figure.
Is it cheaper to drive an electric car than a gas car?
Usually, when charging at home. A car doing 3.5 miles per kWh at $0.17 per kWh costs about 5 cents a mile, against 11 cents a mile for a 30 MPG car at $3.40 a gallon. Public rapid charging at $0.45 per kWh or more narrows or removes the gap, so use the rate you will actually pay.
How should passengers split fuel costs?
The simplest fair split is the total fuel cost divided by everyone in the car, driver included, which is what the per-person figure shows. Some groups exclude the driver, or add a share of tolls and parking; adjust the number of people to match what you agree.
Does driving faster use more fuel?
Yes. Aerodynamic drag rises with the square of speed, so most cars are most efficient at about 50 to 60 mph. Cruising at 75 to 80 mph can use 15 to 25% more fuel than at 60 mph. Use the sensitivity table to see what a 10 or 20% drop in economy would add to the bill.
Is there an in-depth guide to the Fuel Cost Calculator?
Yes. “Fuel Costs, MPG and Tire Sizes: The Driving Maths Explained” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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