How much is 100 miles of gas? Gallons and cost by mpg
About 3.92 gallons, or $16.94, for 100 miles in a typical US gas car: 25.5 mpg (EPA real-world average for new gas cars, MY2024) at $4.319 a gallon (EIA U.S. average price). The sum is 100 / mpg = gallons, then gallons x price. At 20 mpg the same 100 miles take 5 gallons, at 50 mpg only 2. A typical UK petrol car needs 12.7 litres, about £21.35. The tables give every case from the same code as the calculator.
Open the cost per mile calculator
1. Gallons of gas for 100 miles, by mpg
Gallons for 100 miles = 100 / mpg. Cost = gallons x price per gallon. The last column uses the starting price of $4.319 a gallon.
| Fuel economy (mpg) | Gallons | Cost at $4.319 |
|---|---|---|
| 20 | 5 | $21.60 |
| 25 | 4 | $17.28 |
| 25.5* | 3.92 | $16.94 |
| 30 | 3.33 | $14.40 |
| 35 | 2.86 | $12.34 |
| 40 | 2.5 | $10.80 |
| 50 | 2 | $8.64 |
* 25.5 mpg: EPA Automotive Trends Report (MY2024): real-world new-vehicle average 27.2 mpg, 1.7 mpg lower without BEVs and PHEVs = 25.5 mpg for a gas car.
2. Cost of 100 miles of gas by mpg and price per gallon
Each cell is 100 / mpg x price. A dollar more on the gallon adds 100 / mpg dollars to every 100 miles: $5.00 at 20 mpg, $2.00 at 50 mpg.
| Fuel economy (mpg) | $3.00/gal | $3.50/gal | $4.00/gal | $4.319/gal* | $4.50/gal | $5.00/gal |
|---|---|---|---|---|---|---|
| 20 | $15.00 | $17.50 | $20.00 | $21.60 | $22.50 | $25.00 |
| 25 | $12.00 | $14.00 | $16.00 | $17.28 | $18.00 | $20.00 |
| 25.5* | $11.76 | $13.73 | $15.69 | $16.94 | $17.65 | $19.61 |
| 30 | $10.00 | $11.67 | $13.33 | $14.40 | $15.00 | $16.67 |
| 35 | $8.57 | $10.00 | $11.43 | $12.34 | $12.86 | $14.29 |
| 40 | $7.50 | $8.75 | $10.00 | $10.80 | $11.25 | $12.50 |
| 50 | $6.00 | $7.00 | $8.00 | $8.64 | $9.00 | $10.00 |
* Starting values of the calculator: fuel economy 25.5 mpg (EPA Automotive Trends Report (MY2024): real-world new-vehicle average 27.2 mpg, 1.7 mpg lower without BEVs and PHEVs = 25.5 mpg for a gas car); price $4.319 per gallon (EIA Gasoline and Diesel Fuel Update: regular gasoline, U.S. average $4.319/gal, week of 2026-09-14 (released 2026-09-15), read 2026-09-18).
3. Longer trips: 200, 300, 500 miles
The same sum for a road trip, with the US starting values (25.5 mpg, $4.319 a gallon) and for a 30 mpg car.
| Miles | Gallons at 25.5 mpg | Cost at 25.5 mpg | Gallons at 30 mpg | Cost at 30 mpg |
|---|---|---|---|---|
| 100 | 3.9 | $16.94 | 3.3 | $14.40 |
| 200 | 7.8 | $33.87 | 6.7 | $28.79 |
| 300 | 11.8 | $50.81 | 10 | $43.19 |
| 500 | 19.6 | $84.69 | 16.7 | $71.98 |
4. UK: litres of petrol for 100 miles
UK cars show mpg on the imperial gallon (4.54609 litres) and pumps price per litre. Litres for 100 miles = 100 / mpg x 4.54609. The typical UK petrol car (35.8 mpg) needs 12.7 litres, about £21.35 at £1.681 a litre. Per mile, that is 21.3p: the pence per mile figure and the pounds per 100 miles figure are the same number. The guide on the average cost per mile to drive a car in the UK adds insurance, depreciation, servicing and tax.
| Fuel economy (mpg UK) | £1.40/L | £1.50/L | £1.60/L | £1.681/L* | £1.70/L | £1.80/L | £1.90/L |
|---|---|---|---|---|---|---|---|
| 30 | £21.22 | £22.73 | £24.25 | £25.47 | £25.76 | £27.28 | £28.79 |
| 35.8* | £17.78 | £19.05 | £20.32 | £21.35 | £21.59 | £22.86 | £24.13 |
| 40 | £15.91 | £17.05 | £18.18 | £19.10 | £19.32 | £20.46 | £21.59 |
| 45 | £14.14 | £15.15 | £16.16 | £16.98 | £17.17 | £18.18 | £19.19 |
| 50 | £12.73 | £13.64 | £14.55 | £15.28 | £15.46 | £16.37 | £17.28 |
| 60 | £10.61 | £11.37 | £12.12 | £12.74 | £12.88 | £13.64 | £14.40 |
* Starting values of the calculator: fuel economy 35.8 mpg (UK) (European Commission COM(2024) 122, real-world fuel consumption from on-board monitoring, petrol cars registered 2021: 7.89 L/100 km (type-approval 6.38)); price £1.681 per litre (DESNZ Weekly road fuel prices: ULSP (unleaded) 168.14 p/litre, week of 2026-09-14, read 2026-09-18).
5. Gas or all in
For one trip in a car you already own, the gas is what leaves your pocket. For deciding what driving really costs, add the rest: the cost to drive 100 miles guide puts the typical US gas car at $83.67 per 100 miles all in. Type your own mpg, price and yearly miles into the cost per mile calculator to get your figure.
Sources of the starting values: US fuel economy, EPA Automotive Trends Report (MY2024): real-world new-vehicle average 27.2 mpg, 1.7 mpg lower without BEVs and PHEVs = 25.5 mpg for a gas car (2026-09-18); US gas price, EIA Gasoline and Diesel Fuel Update: regular gasoline, U.S. average $4.319/gal, week of 2026-09-14 (released 2026-09-15) (2026-09-18); UK fuel economy, European Commission COM(2024) 122, real-world fuel consumption from on-board monitoring, petrol cars registered 2021: 7.89 L/100 km (type-approval 6.38); EU figure used for the UK (about 35.8 mpg UK), no UK real-world average is published (2026-09-18); UK petrol price, DESNZ Weekly road fuel prices: ULSP (unleaded) 168.14 p/litre, week of 2026-09-14 (2026-09-18). The other rows and columns are round values for comparison, not claims about any car.
Frequently asked questions
- How many gallons of gas is 100 miles?
- 100 divided by your mpg. 5 gallons at 20 mpg, 3.92 gallons at 25.5 mpg (the EPA real-world average for new gas cars), 3.33 at 30 mpg and 2 at 50 mpg. Use the mpg your car shows over a full tank, not the sticker figure, if you have it.
- How much is 100 miles of gas?
- Gallons x price per gallon. With the US starting values (25.5 mpg, $4.319 a gallon) it is $16.94. At 20 mpg and $5.00 it is $25.00; at 50 mpg and $3.00 only $6.00. Table 2 has every pair.
- How much gas is 100 miles in the UK?
- 12.7 litres at 35.8 mpg (UK gallon), about £21.35 at £1.681 a litre (DESNZ weekly average). UK mpg uses the imperial gallon of 4.54609 litres, so litres for 100 miles = 100 / mpg x 4.54609.
- How much gas do I need for 300 or 500 miles?
- Multiply the 100-mile figure. At 25.5 mpg, 300 miles take 11.8 gallons ($50.81 at $4.319) and 500 miles 19.6 gallons ($84.69). Table 3 has the other trips.
- Is gas the whole cost of driving 100 miles?
- No. Gas is the cash you spend on the trip. Depreciation, insurance, maintenance, tyres and tax are paid too, spread over the year. With the US starting values the typical gas car costs $16.94 in gas per 100 miles but $83.67 all in. The guide on what it costs to drive 100 miles and the cost per mile calculator show every item.
More guides
- How much does it cost to drive 100 miles?
Fuel alone and the all-in cost of 100, 200 and 1,000 miles in a typical gas, diesel and electric car, US and UK, by mpg and fuel price, plus 100 miles line by line.
- How much should I charge per mile? Your real cost, US and UK
Charge at least your cost per mile: diesel and petrol fuel by mpg and price, the all-in figure by miles a year, and the IRS and HMRC rates against it. US and UK.
- How much does it cost to own a car per year?
Yearly and monthly cost of a typical gas, diesel and electric car, item by item: fuel, depreciation, insurance, maintenance, tyres and tax. US, UK and EU.
- How much does it cost to drive 100 km?
Fuel for 100 km by L/100 km and price per litre, 100 to 1,000 km all in for petrol, diesel and electric, and km per litre to L/100 km and mpg.
Last updated 2026-09-29. Cost estimates from published starting values (EPA, EIA, AAA, DESNZ, Ofgem, IRS/HMRC), each with its source and date, put through the same arithmetic as the calculators. Your car, prices and mileage move every figure. Information for planning, not financial or tax advice.