Quick answer
Cost per mile = price per gallon ÷ MPG. If you pay $3.50/gal and your car gets 28 MPG, fuel costs you about $0.125 per mile. Multiply by the miles you drive to get the trip, weekly, or annual number.
The formula
One equation does the heavy lifting:
cost_per_mile = price_per_gallon ÷ MPG
total_cost = cost_per_mile × miles_driven
That's it. No spreadsheet, no app needed. The reason it matters: cost per mile lets you compare a sedan, a pickup, a gas car, and a diesel van on the same scale — and lets you compare a $0.20/gal fuel-card discount to a 2 MPG vehicle upgrade.
What you need
- Price per gallon. Use what you actually paid at your last fill — or pull a regional average. FuelHere's fuel cost calculator can pull current EIA averages for you.
- MPG. The window-sticker number is optimistic. Use your last 3–5 fill-ups: gallons divided into miles between fills.
- Miles driven. Per week, per trip, or per year — whichever number you're trying to budget.
A worked example
You commute 320 miles a week in a 30 MPG sedan. Gas is $3.40/gal:
| Input | Value |
|---|---|
| Price / gal | $3.40 |
| MPG | 30 |
| Cost / mile | $0.113 |
| Weekly cost | $36.27 |
| Annual cost | $1,886 |
If a fuel card knocks $0.15 off the gallon, the effective price drops to $3.25, cost per mile drops to $0.108, and you save about $97/year on those same miles.
How fuel cards change the math
A fuel card discount lowers your effective price per gallon; it does not change MPG. So the savings flow directly through the formula:
effective_price = price_per_gallon − discount_per_gallon
cost_per_mile = effective_price ÷ MPG
For a deeper comparison of card programs and rebates, see how fuel card discounts actually work.
How MPG upgrades change the math
A vehicle that gets 32 MPG instead of 28 MPG at $3.50/gal saves about $0.016 per mile. Drive 15,000 miles a year and that's ~$234. The same numbers tell you whether a hybrid pays back, or whether switching a fleet vehicle from gas to diesel is worth the upfront premium — covered in gas vs. diesel.
Why estimates are estimates
The formula is exact; the inputs aren't. Real MPG varies by season, traffic, payload, and tire pressure. Real prices vary by station and brand. Treat any per-mile number — including ours — as a planning estimate, not a guarantee. Verify against your actual receipts before making a financial decision.
Try the calculator
FuelHere's fuel cost calculator applies this formula with real fuel prices, fuel-card discounts, and shareable URLs — so you can hand a manager or a spouse a link instead of a spreadsheet.
