Gas Mileage Calculator
Compute your real-world MPG from miles driven and gallons used — plus cost per mile, total trip fuel cost, and the metric L/100km equivalent.
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Adjust the inputs on the left to see your fuel economy.
Gas mileage — miles per gallon, or MPG — is the single best number for understanding what your car actually costs to drive. Enter the miles you drove and the gallons you burned, and this calculator returns your real-world MPG, what each mile costs you at today's pump price, the total fuel bill for the trip, and the metric L/100km figure used everywhere outside the US.
How it's calculated
MPG = miles driven ÷ gallons used
Cost per mile = price per gallon ÷ MPG
Trip cost = gallons used × price per gallon
L/100km = 235.215 ÷ MPG
Measuring MPG accurately: the fill-to-fill method. Fill your tank completely and reset the trip odometer (or note the mileage). Drive normally. At the next fill-up, fill completely again and divide the trip miles by the gallons shown on the pump. That gallons figure is exactly what you consumed since the last fill, so the math is honest. One tank gives a decent estimate; averaging three or four tanks smooths out pump shutoff variance.
Why your MPG is below the window sticker. EPA ratings come from standardized lab cycles. Real-world economy is typically lower because of cold starts, short city trips, air conditioning, underinflated tires, roof racks, aggressive acceleration, winter fuel blends, and sustained speeds above 70 mph. A 10–15% gap is normal; a sudden larger drop can signal a maintenance issue like a stuck brake caliper or a failing oxygen sensor.
Cost per mile is the most useful planning number: at 25 MPG and $3.50 per gallon, every mile costs 14 cents in fuel alone. Multiply by your annual mileage to budget fuel for the year, or compare two vehicles before buying.
Assumptions and limitations. Results assume US gallons (3.785 L) and statute miles. Fuel is only part of total driving cost — depreciation, insurance, and maintenance are excluded. Set the price slider to 0 if you only want the MPG and metric conversion.
Frequently asked questions
How do I measure my MPG accurately?
Use the fill-to-fill method: fill the tank completely, reset the trip odometer, drive normally, then refill completely. Divide trip miles by the gallons from the second fill. Averaging several tanks gives the most reliable figure.
What is a good MPG?
New US light vehicles average in the mid-to-high 20s overall. Roughly: under 20 MPG is thirsty (trucks, large SUVs), 25–35 MPG is solid for sedans and crossovers, and 40–55+ MPG is hybrid territory.
How do I convert MPG to L/100km?
Divide 235.215 by the MPG value: 25 MPG = 9.4 L/100km, and 47 MPG = 5.0 L/100km. Note the scales run in opposite directions — higher MPG means lower L/100km.
Why is my real MPG lower than the EPA rating?
EPA figures come from lab test cycles. Cold weather, short trips, AC use, low tire pressure, roof cargo, and high-speed driving all cut real-world economy — a 10–15% shortfall is common.
What does cost per mile tell me?
It is your fuel price divided by MPG — the fuel cost of each mile driven. At 25 MPG and $3.50/gallon that is $0.14 per mile, so a 12,000-mile year costs about $1,680 in gas.