Gas Mileage Calculator
Find your car's fuel economy and cost per mile.
Your Details
Breakdown
Visual split of the key components
- Fuel Cost35
Sensitivity
How the result changes across a range
How It Works
- Enter the values on the left.
- Press Calculate to see your results and charts.
- Use Reset to start over from the defaults.
Formula Used
Cost per Mile = Gas Price ÷ MPG.
Good to Know
- • Highway driving typically yields better MPG than city driving.
- • Tire pressure and driving style both affect real-world MPG.
Important Notes
- • This is a single fill-up snapshot, not a long-term average.
- • Actual MPG varies with conditions, load, and driving style.
What Affects Real-World Fuel Economy
EPA-rated MPG figures are measured under standardized conditions and often differ from real-world results. Driving style (hard acceleration vs. smooth), terrain, temperature, tire pressure, and vehicle load can all shift actual mileage noticeably from the rated number. Tracking your own fill-ups over time, as this calculator helps with, gives a more accurate picture than the sticker figure alone.
Turning MPG Into a Budget Number
Once you know your real MPG, cost per mile becomes a useful planning figure — for comparing vehicles, estimating a commute's fuel cost, or budgeting a road trip. It's the same calculation the fuel cost and road trip calculators use, just applied forward instead of worked out from a fill-up.
Defining the Basics
- MPG (miles per gallon) — the standard U.S. measure of fuel economy.
- City vs. highway MPG — separate EPA ratings reflecting different driving conditions.
An Example to Follow: Calculating Real-World MPG
After driving 340 miles on a 11.5-gallon fill-up at $3.50/gallon:
Cost per mile = $3.50 ÷ 29.6 ≈ 11.8¢
Cost of this 340-mile tank ≈ $40.25
Tracking MPG across several fill-ups (rather than just one) smooths out variation from conditions like weather and terrain, giving a more reliable baseline for budgeting fuel costs on future trips.
MPG Cost Comparison Table
Cost per 100 miles at $3.50/gallon:
| MPG | Cost per 100 mi |
|---|---|
| 20 MPG | $17.50 |
| 30 MPG | $11.67 |
| 40 MPG | $8.75 |
What Often Goes Wrong Measuring Fuel Economy
- Using only one fill-up — a single tank can be skewed by unusual driving conditions.
- Not resetting the trip odometer — mixing distances from multiple tanks produces inaccurate MPG.