Fuel Cost Calculator
Fuel cost for a trip is distance divided by fuel economy, multiplied by the price of fuel. A 300-mile drive in a car doing 30 MPG needs 10 gallons — $35.00 at $3.50 a gallon, or about 11.7 cents a mile.
This calculator handles both measurement systems and the conversions between them: distance in miles or kilometres, economy in MPG or L/100km, price per gallon or per litre. Tick round trip and it doubles the distance. Along with the total it gives gallons and litres needed, cost per mile and per kilometre, a rough drive time and the CO2 the fuel will produce.
Enter your details
How to Use the Fuel Cost Calculator
- 1
Enter the distance
Type the one-way distance and choose miles or kilometres. Use the figure from your map app rather than a straight-line distance.
- 2
Enter your fuel economy
Choose MPG or L/100km and enter the figure. Your car trip computer knows this; so does the gas mileage calculator if you would rather work it out from a fill-up.
- 3
Enter the fuel price
Per gallon or per litre, whichever matches the pump. The two are converted internally, so you can mix units freely — kilometres with a price per gallon works fine.
- 4
Tick round trip if you are coming back
This doubles the distance before anything else is worked out. Leave it off for a one-way journey or a move.
How trip fuel cost is calculated
Everything is converted to miles, MPG and price per gallon first, then converted back for display. L/100km becomes MPG through the constant 235.215, and a price per litre is multiplied by 3.78541 to get a price per gallon.
Drive time is a flat distance ÷ 60 mph. It is a sanity check, not a route estimate — it knows nothing about traffic, terrain or stops, and city driving will beat it badly.
The CO2 figure uses 8.887 kg of CO2 per gallon of gasoline burned, the standard EPA tailpipe figure. It covers combustion only, not the emissions from producing and delivering the fuel.
Gallons = distance (miles) ÷ MPG
Total cost = gallons × price per gallon
Cost per mile = total cost ÷ distance
MPG = 235.215 ÷ (L/100km)
CO2 (kg) = gallons × 8.887Worked example: a 300-mile drive
Splitting that with three passengers brings it to under $9 each one-way, which is the comparison most people are actually making when they run this against a train or flight price.
- Distance 300 miles, economy 30 MPG, fuel at $3.50 a gallon.
- Gallons needed: 300 ÷ 30 = 10 gallons (37.85 litres).
- Total cost: 10 × $3.50 = $35.00.
- Cost per mile: $35.00 ÷ 300 = $0.117, or about 7.3 cents per kilometre.
- CO2: 10 × 8.887 = 88.9 kg.
- Round trip: 600 miles, 20 gallons, $70.00 — the per-mile cost does not change.
Cost per 100 miles by fuel economy
At $3.50 a gallon. This is the table that shows why economy matters more on long trips than the pump price does: the jump from 20 to 30 MPG saves more than a 50-cent drop in fuel price.
| MPG | L/100km | Gallons per 100 mi | Cost per 100 mi | Cost per mile |
|---|---|---|---|---|
| 15 | 15.7 | 6.67 | $23.33 | $0.233 |
| 20 | 11.8 | 5.00 | $17.50 | $0.175 |
| 25 | 9.4 | 4.00 | $14.00 | $0.140 |
| 30 | 7.8 | 3.33 | $11.67 | $0.117 |
| 35 | 6.7 | 2.86 | $10.00 | $0.100 |
| 40 | 5.9 | 2.50 | $8.75 | $0.088 |
| 50 | 4.7 | 2.00 | $7.00 | $0.070 |
Getting a realistic number
- Use your own observed MPG, not the window-sticker figure. Real-world economy is commonly 10 to 20% below the rating, and the gap widens with a roof box, a full car or winter fuel.
- Highway driving beats the rating; stop-start city driving falls well short. For a mixed trip, use the lower of your two figures and treat the result as a ceiling.
- A loaded car costs more to move. Four adults and luggage can knock several MPG off a small car.
- Fuel prices vary along a route. For a long drive, use the average of what you expect to pay rather than the price at home.
- This is fuel only. Tolls, parking and the wear-per-mile that makes up most of the real cost of driving are not included.
Features
- Total fuel cost calculation
- Gallons and liters needed
- Cost per mile/kilometer
- Round trip option
- CO2 emissions estimate
- Trip time estimation
Frequently Asked Questions
How much gas will I use on a road trip?
Divide the trip distance by your miles per gallon. A 450-mile trip at 25 MPG needs 18 gallons. Multiply by the price per gallon for the cost: 18 × $3.50 = $63.00. Tick round trip to double the distance first.
How do I calculate cost per mile?
Divide the fuel price by your MPG. At $3.50 a gallon and 28 MPG that is 12.5 cents per mile. This is fuel only — the full cost of running a car, including depreciation, tyres and servicing, is several times higher.
Can I use kilometres and litres?
Yes, and you can mix them. Distance takes miles or kilometres, economy takes MPG or L/100km, and price takes per gallon or per litre, each chosen separately. The calculator converts internally and shows both gallons and litres in the result.
How is the drive time worked out?
It divides the total distance by a flat 60 mph. That makes it a rough reference for highway driving only — it does not account for traffic, speed limits, terrain or stops, so treat it as a lower bound.
How much CO2 does a gallon of gasoline produce?
About 8.887 kg of CO2 per gallon burned, the EPA tailpipe figure used here. A 300-mile trip at 30 MPG produces roughly 89 kg. The figure covers combustion only; producing and transporting the fuel adds roughly another fifth on top.
Does this work for a diesel or hybrid car?
Yes for the arithmetic — enter the car MPG and the diesel price and the cost is correct. The CO2 figure assumes gasoline, so it understates diesel, which produces about 10.18 kg of CO2 per gallon.
Last reviewed