Enter the miles driven since the last fill, the gallons added at the next fill-up and the fuel price per gallon. Fill the tank to the same point each time, such as the pump's first click-off, and reset the trip meter at each fill. One tank is a rough number, so average several.
The tool also reports the fuel cost per mile and the liters per 100 kilometers used outside the United States.
MPG: worked example
| Miles driven | 350 |
|---|---|
| Gallons of fuel used | 12.5 |
| Fuel price per gallon | $3.50 |
| Miles per gallon | 28 |
| Fuel cost per mile | $0.13 |
| Liters per 100 km | 8.4 |
MPG: changing Miles driven
| Miles driven | Miles per gallon | Fuel cost per mile | Liters per 100 km |
|---|---|---|---|
| 280 | 22.4 | $0.16 | 10.5 |
| 315 | 25.2 | $0.14 | 9.3 |
| 350 (example) | 28 | $0.13 | 8.4 |
| 385 | 30.8 | $0.11 | 7.6 |
| 420 | 33.6 | $0.10 | 7 |
MPG: compare input ranges
| Input | Tested from | To | Miles per gallon: low input | Miles per gallon: high input | Swing |
|---|---|---|---|---|---|
| Gallons of fuel used | 11 | 14 | 31.8 | 25 | 6.8 (24%) |
| Miles driven | 315 | 385 | 25.2 | 30.8 | 5.6 (20%) |
| Fuel price per gallon | $3.15 | $3.85 | 28 | 28 | 0 |
MPG: individual input comparisons
| Input | Value | Miles per gallon | Fuel cost per mile | Liters per 100 km |
|---|---|---|---|---|
| Miles driven | 280 | 22.4 | $0.16 | 10.5 |
| 315 | 25.2 | $0.14 | 9.3 | |
| 350 | 28 | $0.13 | 8.4 | |
| 385 | 30.8 | $0.11 | 7.6 | |
| 420 | 33.6 | $0.10 | 7 | |
| Gallons of fuel used | 10 | 35 | $0.10 | 6.7 |
| 11 | 31.8 | $0.11 | 7.4 | |
| 13 | 26.9 | $0.13 | 8.7 | |
| 14 | 25 | $0.14 | 9.4 | |
| 15 | 23.3 | $0.15 | 10.1 | |
| Fuel price per gallon | $2.80 | 28 | $0.10 | 8.4 |
| $3.15 | 28 | $0.11 | 8.4 | |
| $3.50 | 28 | $0.13 | 8.4 | |
| $3.85 | 28 | $0.14 | 8.4 | |
| $4.20 | 28 | $0.15 | 8.4 |
MPG: combined input changes
| Miles driven / Gallons of fuel used | 10 | 13 | 15 |
|---|---|---|---|
| 280 | 28 | 21.5 | 18.7 |
| 315 | 31.5 | 24.2 | 21 |
| 350 | 35 | 26.9 | 23.3 |
| 385 | 38.5 | 29.6 | 25.7 |
| 420 | 42 | 32.3 | 28 |
MPG: which assumptions move the result?
MPG: values and definitions
| Quantity and definition | Value used |
|---|---|
| Miles driven | 350 |
| Gallons of fuel used — Gallons added at the fill-up that follows the miles driven. | 12.5 |
| Fuel price per gallon | $3.50 |
| Miles per gallon | 28 |
| Fuel cost per mile | $0.13 |
| Liters per 100 km | 8.4 |
MPG: half and double Gallons of fuel used
| Gallons of fuel used | Miles per gallon |
|---|---|
| 6.3 | 56 |
| 12.5 | 28 |
| 25 | 14 |
Tank-to-tank figures vary with the pump shutoff and temperature, and the car's own display can read a few percent high. Short trips, cold weather, towing, roof racks and aggressive driving lower efficiency. MPG is not a linear measure of fuel use, so a gain from 15 to 20 saves more fuel than a gain from 30 to 35.
MPG: formula
Common error: Trusting one tank. Weather, traffic and a trip mix all move mileage, so average three or four fill-ups before comparing with the sticker.
Energy & Utilities calculators: Battery Runtime Calculator, Solar Panel Output Calculator, Solar Payback Calculator, LED Bulb Savings Calculator, Generator Size Calculator, Electricity Cost Calculator.
Real mileage comes from one full tank to the next, not from a single reading on the dash. Divide the miles driven by the gallons it took to refill, and 350 miles on 12.5 gallons is exactly 28 miles per gallon. Cost per mile converts that into money, and the liters per 100 kilometers figure lets you compare with the metric numbers on foreign specs.
Fill to the same click of the pump each time. Uneven fill-ups swing a single tank's result by several miles per gallon.
Compare with electric costs on the EV charging cost calculator, estimate a trip on the speed, distance and time page and see running costs on the car loan and lease pages. The fuel cost and unit converters change gallons and liters.
How do I calculate miles per gallon?
Divide the miles driven by the gallons of fuel used, measured from one fill-up to the next.
What is 28 MPG in liters per 100 km?
Divide 235.215 by the MPG. So 28 MPG is about 8.4 liters per 100 kilometers.
Why is my real MPG lower than the sticker?
Speed, weather, short trips, load and driving style all reduce economy below the test conditions used for the rating.