Cost per mile is a different number from total trip cost — it’s what lets you compare vehicles, routes, or reimbursement rates fairly, regardless of how long a specific trip is.
Wondering if it’s cheaper to take your car or a rental? Or how your car’s running costs stack up against the standard mileage reimbursement rate? The number you actually need is cost per mile — not a one-off trip total.
The Cost-Per-Mile Formula
Cost per mile = fuel price per gallon ÷ miles per gallon
That’s it — no trip distance needed at all, since cost per mile is a rate, not a total. For example:
- fuel price = $3.50 per gallon
- vehicle efficiency = 25 MPG
$3.50 ÷ 25 = $0.14 per mile
Once you have that single number, multiplying it by any distance instantly gives you a cost for that specific trip — no need to redo the division each time.
Why Cost Per Mile Matters More Than a Trip Total
A single trip’s total fuel cost only tells you about that one trip. Cost per mile is what actually lets you compare things fairly:
- Comparing two vehicles — a truck at $0.22/mile versus a sedan at $0.13/mile, regardless of trip length
- Deciding whether to rent or drive your own car — compare your cost per mile against a rental’s daily rate plus its fuel cost
- Checking a mileage reimbursement rate — many employers and tax authorities publish a standard cents-per-mile rate; comparing it to your actual fuel cost per mile shows whether it covers just fuel or also wear and maintenance
- Budgeting recurring driving — a daily commute’s monthly cost is just cost per mile × miles driven per month
Fuel-Only vs. True Cost Per Mile
The formula above gives your fuel-only cost per mile. Standard mileage reimbursement rates (like the ones used for tax deductions or employee reimbursement) are usually higher than fuel-only cost per mile, because they also fold in an estimate for:
- tires and routine maintenance
- depreciation
- insurance
If you’re comparing your own fuel cost per mile against a published reimbursement rate, remember you’re comparing a partial number (fuel only) against a fuller one — the gap between them isn’t a discrepancy, it’s the other ownership costs the reimbursement rate is meant to cover.
Cost Per Mile in Liters and Kilometers
If your vehicle’s efficiency is given in L/100 km instead of MPG:
Cost per km = (L/100 km ÷ 100) × price per liter
For example, a car using 7 L/100 km with fuel at $1.60 per liter: (7 ÷ 100) × $1.60 = $0.112 per kilometer.
Get Your Number Instantly
The Notchful Fuel Cost Calculator shows both your total trip cost and your cost-per-mile figure side by side from the same three inputs — distance, fuel economy, and fuel price — so you get both numbers at once instead of calculating them separately.
FAQ
How do I calculate my car’s cost per mile?
Divide your fuel’s price per gallon by your vehicle’s miles-per-gallon rating. The result is your fuel-only cost per mile.
Is cost per mile the same as a mileage reimbursement rate?
No. A published reimbursement rate typically includes maintenance, depreciation, and insurance on top of fuel, so it’s usually higher than your fuel-only cost per mile.
Does cost per mile change with speed or driving style?
Yes — real-world fuel economy varies with speed, terrain, weather, and driving style, so your actual cost per mile can shift even if fuel price and your car’s rated MPG stay the same.
How is this different from calculating total road trip fuel cost?
Total trip cost answers “what will this specific trip cost.” Cost per mile is a reusable rate that lets you compare vehicles, routes, or reimbursement rates without redoing the math for every distance. If you just need a one-off trip total, see our road trip fuel cost guide instead.
Final Takeaway
Cost per mile = price per gallon ÷ miles per gallon. It’s the single reusable number behind vehicle comparisons, rental-versus-own decisions, and reimbursement-rate checks — multiply it by any distance to get a trip total whenever you need one.
Written by the Notchful team. Last updated: September 2026.