Fuel Cost Calculator (Trip Gas Price)
Gallons needed, total fuel spend, cost per mile, and the per-passenger split for one-way or round trips — in MPG or L/100km with any currency fuel price.
Fuel Cost — interactive calculator, computed instantly in your browser.
Road Trip Fuel Cost: MPG, Gas Price, and the Real Cost per Mile
600 mi ÷ 30 MPG = 20 gal × $3.50 = $70
Fuel cost for a trip is three numbers multiplied: distance ÷ efficiency × price. The calculator handles one-way and round trips, MPG or L/100km efficiency, any currency price per gallon or liter, and splits the total across passengers — plus cost per mile and a CO₂ line for the full picture.
1. Gallons = Distance ÷ MPG
- 600 miles at 30 MPG = 20 gallons → $3.50/gal = $70
- Round trip doubles distance, not efficiency — check the box and the gallons double with it
- MPG is not linear: doubling from 20 to 40 MPG saves far more fuel on a long trip than 30 to 35
- City stop-and-go degrades real MPG 10–20% below the window sticker; highway beats it slightly
2. L/100km and the Unit Trap
- L/100km measures consumption (lower is better): 7 L/100km ≈ 33.6 US MPG (235.2 ÷ value)
- km/L is the metric MPG analogue: liters per 100 km invert to km per liter
- A US gallon is 3.785 L; an imperial gallon is 4.546 L — US and UK MPG figures are not comparable
- Mixed units are the classic error: the calculator converts distance to what your efficiency unit expects
3. Price, Passengers, and Seasonality
- Gas prices move daily — use today's local price, not last summer's memory; the price field accepts any currency unit
- Passengers divide fuel cost only: tolls, lodging, and food split by their own rules
- Rental cars bill mileage separately — multiply excess miles by the per-mile rate in this calculator
- Altitude, roof boxes, and hauling drop MPG 5–15% — enter the real efficiency, not the brochure number
4. Cost per Mile and Vehicle Comparison
Dividing total fuel by distance gives fuel cost per mile — the number that makes vehicle comparisons honest. At 30 MPG and $3.50/gal it is 11.7¢/mile; at 20 MPG it is 17.5¢. That gap over 12,000 annual miles is roughly $700/year, before maintenance and depreciation. Each gallon burned also releases about 8.887 kg of CO₂, which the calculator prints alongside the money.
🔗 Distance Math Cross-References
Fuel cost is distance ÷ efficiency × price — the three inputs are the core of the 🔄 Conversion Hub converters.
MPG describes the car, cost describes the trip: run both when comparing vehicles or splitting a road-trip bill with passengers.
Frequently Asked Questions (Fuel Cost)
Divide total distance by your MPG to get gallons, then multiply by the price per gallon: 600 miles ÷ 30 MPG = 20 gallons × $3.50 = $70. Tick round trip to double the distance, enter your actual gas price, and split across passengers if you are sharing the car.
At 30 MPG and $3.50 per gallon, fuel costs about 11.7 cents per mile. A 20 MPG vehicle costs 17.5 cents at the same price. This covers fuel only — insurance, maintenance, and depreciation add several times more to true ownership cost per mile.
US MPG = 235.2 ÷ L/100km. So 7 L/100km ≈ 33.6 MPG, and 10 L/100km = 23.5 MPG. Remember L/100km runs the opposite direction — lower is more efficient — and UK MPG uses the larger imperial gallon (282.5 ÷ L/100km).
City traffic, idling, climate control, roof racks, and tire pressure all push real consumption above the rated MPG — usually 10–20%. Enter the efficiency your trip computer actually reports over a similar route, and use today's pump price rather than a stale average.