Trip & budget
How much fuel does 100 miles use? A simple guide
A 100-mile trip is a useful benchmark. It is long enough to show real differences between cars, but short enough to calculate without a spreadsheet. The answer depends on the MPG figure and, in the UK, on converting miles to litres.
Quick answer
In the US, fuel used = 100 ÷ MPG US gallons. At 25 MPG that is 4 gallons. In the UK, fuel used = 100 ÷ MPG UK × 4.54609 litres. At 50 MPG UK that is about 9.09 litres.
Key takeaways
- US: gallons = miles ÷ MPG US.
- UK: litres = miles ÷ MPG UK × 4.54609.
- Multiply fuel used by the price you pay to get cost.
US calculation
If a car returns 25 MPG US, it uses 4 gallons to cover 100 miles. At $3.50 per gallon, the fuel cost is $14.00. At 40 MPG US, it uses 2.5 gallons, or $8.75 at the same price.
| MPG US | US gallons | Litres (approx.) |
|---|---|---|
| 20 | 5.0 | 18.9 |
| 25 | 4.0 | 15.1 |
| 30 | 3.33 | 12.6 |
| 40 | 2.5 | 9.46 |
| 50 | 2.0 | 7.57 |
UK calculation
In the UK, the same 100 miles is divided by MPG UK to get imperial gallons, then multiplied by 4.54609 to get litres. At 50 MPG UK, the trip uses about 9.09 litres. At 145p per litre, that costs about £13.18.
If you use a US MPG figure by mistake, the litre estimate will be too low because the US gallon is smaller.
Turn fuel into cost
The cost step is the same in both systems: fuel used × price per unit. Keep the units together. A price per litre cannot be applied to a number of gallons without converting first.
Questions
How many litres does 100 miles use?
How much does 100 miles cost?
Is 100 miles the same as 100 km?
Sources
- GOV.UK — weekly road fuel prices — UK price statistics for context, not a live station price.
- US EIA — gasoline and diesel prices — US regional and national averages.
- European Commission — Weekly Oil Bulletin — EU fuel price monitoring.
- fueleconomy.gov — US fuel-economy ratings — EPA label values, test-cycle context and consumer guidance.
Try the calculator
Related guides
Fuel cost for 100 km: formula and examples
Calculate litres and fuel cost for 100 kilometres using L/100 km or km/L, with examples for Europe and Asia-Pacific markets.
Cost per mile formula: a plain-English guide
Calculate fuel cost per mile correctly for UK and US units, with examples and the mistake that makes estimates too low.
Round-trip fuel cost formula
A simple method for round-trip fuel estimates, including detours, unit changes and the difference between one-way and return distance.
A note on prices and rules
Page last reviewed: . Formulas are covered by automated tests. Prices are inputs, not live data.