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Auto & Vehicle
Gas Mileage Calculator — MPG, Cost Per Mile & L/100km
Turn miles driven and gallons pumped into true MPG, cost per mile, and L/100km
Gas mileage — miles per gallon, or MPG — is the single most useful number a US driver can know about their car. The EPA window sticker gives you an estimate, but your real-world mileage depends on how and where you drive: a lead foot on the highway, short cold-start commutes around town, a roof box on a road trip, underinflated tires, or a cargo bed full of tools all move the needle. The only way to know your true MPG is to measure it at the pump, and that is exactly what this calculator does.
The method is the classic tank-to-tank fuel log. Fill the tank all the way up and reset your trip odometer (or write down the odometer reading). Drive normally until you need gas again, then fill all the way up a second time. The pump tells you how many gallons it took to refill, and your trip odometer tells you how many miles you drove on that fuel. Divide one by the other:
MPG = miles driven ÷ gallons used.
Example: you drove 300 miles and it took 12 gallons to refill. 300 ÷ 12 = 25 MPG.
Once you know your MPG, two more numbers fall right out of it. Cost per mile tells you what every mile actually costs in fuel: price per gallon ÷ MPG. At $3.50 a gallon and 25 MPG, that's 3.50 ÷ 25 = $0.14 per mile — handy for budgeting a commute, pricing a side-gig delivery run, or figuring out a mileage reimbursement. And for anyone comparing against an import spec or a European review, the metric L/100km = 235.215 ÷ MPG converts your figure to liters per 100 kilometers; 25 MPG ≈ 9.4 L/100km.
This is a fuel-efficiency calculator, not a trip-cost planner. If you already know your MPG and just want the dollar total for a specific drive — say, 400 miles to grandma's house — use the companion fuel-cost calculator instead. Use this one to discover or verify the MPG number in the first place, to watch how your mileage drifts across seasons, and to catch a real problem early: a sudden 15% drop in MPG often means low tire pressure, a dragging brake, a clogged air filter, or a failing oxygen sensor long before a dashboard light comes on.
📖 See also: How to Calculate Your Car Payment
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• MPG = miles driven ÷ gallons used • Cost per mile = price per gallon ÷ MPG • L/100km = 235.215 ÷ MPG (metric readout) • To estimate the fuel cost of a specific trip, use the Fuel Cost Calculator
📰 Formula
• MPG = miles driven ÷ gallons used • Cost per mile = price per gallon ÷ MPG • L/100km = 235.215 ÷ MPG (metric readout) • To estimate the fuel cost of a specific trip, use the Fuel Cost Calculator
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Dividing gallons by miles instead of miles by gallons — that gives gallons per mile, not MPG.
- Not filling the tank all the way on both stops, so the gallons don't match the miles driven.
- Forgetting to reset the trip odometer, then guessing the mileage for the tank.
- Mixing units — entering kilometers or liters into a miles-and-gallons calculator.
- Confusing the EPA combined estimate with your actual measured mileage.
💡 Tips
- For an accurate reading, fill all the way to the first click on both the start and end fill-ups, then reset the trip meter.
- Average several tanks across different conditions — one highway road trip will flatter your number versus stop-and-go city driving.
- A sudden MPG drop of 10–15% is an early warning: check tire pressure, air filter, and for a dragging brake before anything else.
- Cost per mile is the fastest way to compare two cars or to set an honest mileage rate for gig work.
Embed this calculator on your site
Copy the code below and paste it into the HTML of your site or blog.
<iframe src="https://www.calcnimbus.com/embed/gas-mileage-calculator" width="100%" height="500" frameborder="0" style="border:1px solid #eee;border-radius:12px"></iframe>
❓ Frequently asked questions
How do I calculate my gas mileage (MPG)?
Divide the miles you drove by the gallons it took to refill the tank. If you went 300 miles and it took 12 gallons, that's 300 ÷ 12 = 25 MPG.
What is a good MPG for a car?
It varies by vehicle type. Many compact sedans land around 30–40 MPG combined, midsize SUVs around 22–28 MPG, and full-size trucks around 17–22 MPG. Hybrids often top 45–55 MPG. Compare your measured number to your car's EPA combined rating.
How do I figure out my fuel cost per mile?
Divide the price per gallon by your MPG. At $3.50 a gallon and 25 MPG, each mile costs 3.50 ÷ 25 = $0.14 in fuel.
How do I convert MPG to L/100km?
Use L/100km = 235.215 ÷ MPG. For example, 25 MPG = 235.215 ÷ 25 ≈ 9.4 L/100km. Note that lower L/100km means better efficiency, the opposite of MPG.
Why is my real MPG lower than the EPA window sticker?
The EPA figures come from standardized lab cycles. Real driving — cold starts, short trips, highway speeds above 65 mph, A/C use, cargo, hills, and low tire pressure — usually lands a few MPG below the sticker.
How many tanks should I average for an accurate number?
At least three to five full tanks across a mix of city and highway driving. A single tank can be skewed by one long highway trip or a week of heavy traffic.
Does this calculator work for highway vs. city mileage?
Yes — just log a tank that's mostly highway and a tank that's mostly city separately, then enter each one. You'll see how much your MPG swings between the two.
What's the difference between this and a fuel-cost calculator?
This calculator finds your MPG and your cost per mile from a tank of gas. A fuel-cost calculator goes the other way: you give it a trip distance and your known MPG, and it returns the total dollars of gas that trip will burn.
Can I use this to set a mileage reimbursement rate?
It gives you the fuel portion (cost per mile). The IRS standard mileage rate also bundles in depreciation, insurance, and maintenance, so it's higher than fuel alone. This is an estimate, not tax advice — check the current IRS rate for reimbursements.