Fuel Cost Calculator — Work Out the Gas Cost of Any Trip
Enter your distance, fuel economy and pump price to get the exact fuel cost of a trip, a commute or a whole year of driving — in US MPG, UK MPG or litres per 100 km, with the cost split per passenger.
Tip: use the price you actually pay at your regular station, not the national average.
Enter your distance, economy and fuel price to see the cost.
Why this fuel cost calculator is more useful than a gas price lookup
Knowing the price at the pump tells you almost nothing about what a journey actually costs. What matters is the interaction between distance, fuel economy and price — and whether that cost is worth splitting, absorbing or designing away with a different vehicle. This calculator handles all three questions on one screen.
Three calculations, one tool
A single trip, a full year of commuting, or a head-to-head between the car you own and the car you are thinking about. Most sites make you visit three different pages.
US MPG, UK MPG and L/100km
Switch systems and your figures convert with you, including the fuel price basis. A UK gallon is 4.546 litres against the US gallon’s 3.785, and this tool respects the difference instead of quietly mixing them.
Split the cost per passenger
Enter how many people are travelling and get a fair per-person figure you can send to the group chat before you set off, not after.
Cost per mile, not just a total
Cost per mile or per kilometre is the number that makes journeys comparable, supports mileage claims and tells you what a detour really costs.
A live efficiency gauge
The gauge shows where your vehicle sits between thirsty and efficient, and always displays the equivalent figure in the other unit system.
Fast, private, no sign-up
Everything runs in your browser. Nothing is uploaded, there is no account, and results update as you type — even on a slow connection at a service station.
How to use the fuel cost calculator
Choose your unit system
US MPG for the United States, UK MPG for Britain and Ireland, or L/100km for most of Europe, Asia, Australia and Canada. Your entered numbers convert automatically when you switch.
Pick trip, commute or comparison
Trip cost is for a one-off journey, commute cost turns a daily drive into a weekly, monthly and annual figure, and the comparison mode shows what a more efficient car would save you.
Enter distance, economy and price
Use your car’s real-world economy rather than the brochure figure — the trip computer average over a full tank is usually within a few percent. Then set your currency and the price you actually pay.
Read and share the result
The headline is your fuel cost. Below it you get fuel volume, cost per mile or kilometre, the per-person split and the equivalent economy in the other unit system. Tap Copy results to share the breakdown.
The formulas and conversions used
Fuel cost is a two-step calculation: work out how much fuel the distance consumes, then multiply by the price per unit of fuel. The only trap is mixing unit systems, which is why the three are kept strictly separate here.
| System | Fuel used | Cost | Worked example |
|---|---|---|---|
| US MPG | Miles ÷ MPG = US gallons | Gallons × price per gallon | 500 mi ÷ 30 MPG = 16.67 gal × $3.20 = $53.33 |
| UK MPG | Miles ÷ MPG = imperial gallons | Gallons × price per imperial gallon | 500 mi ÷ 36 MPG = 13.89 gal |
| Metric | km × L/100km ÷ 100 = litres | Litres × price per litre | 800 km × 7.8 ÷ 100 = 62.4 L |
MPG to L/100km conversion table
The conversion is L/100km = 235.215 ÷ US MPG. Note that the relationship is inverse, so improving from 15 to 20 MPG saves far more fuel than improving from 40 to 45 MPG over the same distance.
| US MPG | UK MPG | L/100km | Fuel for 100 miles |
|---|---|---|---|
| 20 | 24.0 | 11.76 | 5.00 US gal |
| 25 | 30.0 | 9.41 | 4.00 US gal |
| 30 | 36.0 | 7.84 | 3.33 US gal |
| 35 | 42.0 | 6.72 | 2.86 US gal |
| 40 | 48.0 | 5.88 | 2.50 US gal |
| 50 | 60.0 | 4.70 | 2.00 US gal |
Useful unit equivalents
| Unit | Equivalent |
|---|---|
| 1 US gallon | 3.785 litres |
| 1 imperial (UK) gallon | 4.546 litres |
| 1 UK MPG | 0.833 US MPG |
| 1 mile | 1.609 kilometres |
How to cut the number this calculator gives you
Once you know your cost per mile, the levers that move it become obvious. These are the changes with the largest measured effect on real-world fuel consumption.
- Ease off the highway speed. Aerodynamic drag rises with the square of speed, so cruising at 65 instead of 75 mph typically cuts consumption by 10–15% on a long run.
- Drive smoothly. Hard acceleration and late braking can add 10–30% to highway consumption and considerably more in town.
- Take the roof box off when you are not using it. An empty roof rack or box can add 10–25% on the highway purely through drag.
- Check tyre pressures monthly. Significantly underinflated tyres increase rolling resistance and quietly add a few percent to every journey.
- Stop idling. A warm engine burns fuel for nothing at a standstill, so switch off for waits longer than a minute.
- Combine errands into one trip. A cold engine uses noticeably more fuel for the first few miles, so three short separate trips cost far more than one longer loop.
- Lose the dead weight. Every extra 100 lb in the boot costs roughly 1% in economy, which compounds over a year of commuting.
Fuel cost calculator FAQs
How do I calculate the fuel cost of a trip?
How much gas does a 500-mile trip cost?
How do I convert MPG to litres per 100 km?
Why is UK MPG higher than US MPG for the same car?
How much does my commute cost per year?
How much would a more efficient car save me?
What is a reasonable fuel cost per mile?
Does driving slower really save fuel?
Related calculators
Know what the journey costs before you turn the key
Enter your distance, your real-world economy and the price you pay, and you have a fuel figure you can budget with, split with passengers or claim back. Scroll up, pick the tab that matches your question and copy the breakdown.
Results are estimates based on the figures you enter. Real consumption varies with traffic, load, terrain, weather and driving style.