How it works
Trip fuel cost starts from three numbers: distance, fuel economy (miles per gallon) and price per gallon. Gallons required = distance ÷ mpg. Total cost = gallons × price per gallon. Cost per mile = total cost ÷ distance — useful for comparing vehicles or reimbursing mileage. Worked example: 300-mile trip, 25 mpg, $3.50/gallon. Gallons = 300 ÷ 25 = 12.0 gallons. Fuel cost = 12 × $3.50 = $42.00. Cost per mile = $42 ÷ 300 = $0.14/mile. Real-world mpg varies with speed, load, AC use and terrain — highway EPA ratings often exceed mixed driving; towing or mountain passes reduce economy sharply. Round-trip cost doubles one-way distance unless you enter the full loop mileage. Compare against the IRS standard mileage rate (deduction/reimbursement benchmark, updated annually) for business travel — fuel-only cost ignores depreciation, insurance and maintenance that full mileage rates cover. For metric trips, convert kilometres to miles (÷ 1.609) or use local litres/100 km figures converted to mpg before entry.
Formula
Gallons = distance ÷ mpg | Fuel cost = gallons × price/gal | Cost/mile = fuel cost ÷ distance
Tips
- Use your actual tank average mpg, not the window sticker, for long-trip accuracy.
- Add 15–20% fuel buffer for traffic, detours and idling on unfamiliar routes.
- Compare cost per mile across cars when deciding which vehicle to take.
- Gas prices vary by state — update price per gallon for the states you drive through.
Frequently asked questions
- How much gas for 300 miles at 25 mpg?
- 12 gallons. At $3.50/gallon that is $42.00 total, or $0.14 per mile.
- How do I improve trip fuel estimates?
- Use real-world mpg from your last fill-up (miles driven ÷ gallons pumped) instead of EPA combined rating.
- Does this include tolls and wear?
- No — only fuel. Full trip cost adds tolls, lodging and vehicle depreciation.
- Round trip or one way?
- Enter one-way miles for a single leg; double the distance (or run twice) for round trips.