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Gas Mileage Calculator

Free gas mileage calculator to find your miles per gallon (MPG) and estimate trip fuel cost. Perfect for road trip planning and tracking average MPG over time.

Total distance traveled for this tank/trip

Amount of fuel used over that distance

In your local currency/unit — used to estimate trip fuel cost

What Is the Gas Mileage Calculator?

The Gas Mileage Calculator is a free online tool that calculates your vehicle's fuel economy in miles per gallon (MPG) based on the distance you drove and the fuel you used. It also estimates your trip fuel cost if you provide a price per gallon, making it a handy tool for road trip budgeting, comparing vehicles, or simply tracking how efficiently your car is running over time.

How to Use the Gas Mileage Calculator

  1. Enter miles driven — the distance covered since your last fill-up (or for your whole trip)
  2. Enter gallons of fuel used — how much fuel it took to cover that distance
  3. Optionally enter a price per gallon (in your local currency/unit) to estimate the fuel cost for that distance
  4. Click "Calculate MPG" to see your fuel economy and a comparison table across common MPG values

The Formulas Used

The calculator uses two straightforward formulas:

CalculationFormula
Miles per GallonMPG = Miles Driven ÷ Gallons Used
Trip Fuel CostCost = Gallons Used × Price per Gallon

The price-per-gallon field accepts a plain number in whatever currency or unit you use locally — the calculator doesn't assume any particular currency, so the result is shown as a plain number in the same unit you entered.

Worked Example

Suppose you drove 300 miles and used 10 gallons of fuel to do it. Your fuel economy is 300 ÷ 10 = 30 MPG. If fuel costs 3.50 per gallon where you are, your fuel cost for that distance is 10 × 3.50 = 35.00. These numbers update instantly as you adjust any of the three inputs.

Practical Notes

  • For the most accurate MPG, fill your tank completely at both the start and end of the measurement period, and use the odometer reading (not a trip estimate) for miles driven.
  • MPG naturally varies between city and highway driving — highway driving is usually more fuel-efficient for most vehicles.
  • Track several fill-ups over time and average the results for a more reliable picture of your vehicle's real-world fuel economy than a single tank.
  • The MPG comparison table below your results shows how many gallons (and how much cost) the same trip distance would require at various fuel-economy levels — useful when shopping for a more efficient vehicle.

Planning other parts of a trip or project? Try our length converter or weight converter for other everyday unit conversions.

Frequently Asked Questions

How do I calculate miles per gallon?
Divide the total miles driven by the gallons of fuel used: MPG = Miles ÷ Gallons. For example, if you drove 300 miles and used 10 gallons of fuel, your fuel economy is 300 ÷ 10 = 30 MPG.
How can I use this as a gas mileage calculator for a road trip?
Fill your tank at the start of your trip and note the odometer reading. When you refuel, enter the miles driven since the last fill-up and the gallons it took to refill the tank. The calculator will show your MPG for that leg of the trip, plus an estimated fuel cost if you enter a price per gallon.
How do I calculate fuel cost for a trip?
Multiply the gallons of fuel you'll use by the price per gallon: Fuel Cost = Gallons × Price per Gallon. If you know your car's MPG, you can also estimate gallons needed as Trip Distance ÷ MPG, then multiply by the price per gallon.
What is a good average MPG for a car?
It varies widely by vehicle type. Compact and hybrid cars often average 35-50+ MPG, midsize sedans typically get 25-35 MPG, and larger SUVs or trucks often average 15-25 MPG. Check your vehicle's EPA fuel economy rating for a more precise baseline.
Does this calculator work for liters and kilometers too?
This calculator is set up for miles and gallons (the standard fuel economy units in the US). If your vehicle's dashboard shows liters per 100 km, you'll need to convert those figures to miles and gallons first, or think of MPG conversion as a separate metric system calculation.
Why does my MPG vary between fill-ups?
Fuel economy fluctuates due to driving style, terrain (hills vs. flat roads), traffic conditions, weather, tire pressure, vehicle load, and whether you're driving mostly highway or city miles. Tracking multiple fill-ups and averaging them gives a more reliable picture than a single tank.
How do I estimate fuel cost before a long road trip?
Estimate your trip distance, divide by your car's average MPG to get gallons needed, then multiply by the current price per gallon along your route. This calculator's MPG comparison table shows gallons needed and cost across a range of MPG values, which is handy for planning.
Can I use this calculator to compare two vehicles?
Yes. Run the calculation separately for each vehicle's miles-driven and gallons-used figures, then compare the resulting MPG and estimated fuel costs side by side to see which is more fuel-efficient or cost-effective for your typical driving.

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How this is calculated: This tool uses standard, well-established formulas for unit conversion calculations. Results are estimates for informational and planning purposes — always double-check figures for anything with real-world consequences (e.g. ordering materials or submitting grades).