Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate your vehicle's real-world fuel economy from miles driven and gallons used.
This tool calculates your vehicle's actual fuel economy as miles driven ÷ gallons used -- more accurate for your real driving conditions than a manufacturer's rated MPG, since it reflects your actual routes, driving style, and vehicle condition.
Enter the miles driven since your last fill-up and the gallons it took to fill up again. Your real-world MPG appears instantly.
The calculation is a plain division of miles driven by gallons used, shown to two decimal places. If gallons is zero or negative the tool returns zero. The accuracy of the result depends entirely on how carefully you measure the two inputs, so the method you use to record them matters more than the arithmetic itself.
MPG = miles driven / gallons used
The gallons you add at the second fill-up are the fuel used since the first. Do not count the gallons from the first fill-up, since that fuel was consumed before your measurement began.
Say you drove 312 miles and the refill took 11.2 gallons. Dividing gives about 27.86 MPG. A second tank with 290 miles on 11.6 gallons gives 25.0 MPG. Averaging the two by simply averaging 27.86 and 25.0 is a common shortcut, but a more accurate method adds all the miles and all the gallons: 602 miles over 22.8 gallons is about 26.4 MPG. Combining totals prevents a short tank with unusual driving from carrying too much weight.
If a tank gives a number far above or below your usual range, check for a data-entry slip first, such as forgetting a digit in the miles. A sudden decline across several tanks can point to something worth checking, like low tire pressure, an aging air filter, or a dragging brake. That is not a diagnosis, just a nudge to have a mechanic look at the vehicle if the change persists. Some cars also report a trip computer MPG that reads a little optimistic, so measuring by hand is a good cross-check.
Once you have a reliable figure, use it in the Gas Cost Calculator to plan a trip, the Fuel Cost per Mile Calculator to compare vehicles, or the MPG to L/100km Converter if you need the metric equivalent for comparing with international specifications.
Manufacturer ratings are measured under standardized test conditions -- real-world MPG varies with driving style, terrain, weather, tire pressure, and load, so some difference from the rated figure is normal.
It is better to. A single tank can be skewed by an unusual trip or an inconsistent fill. Total the miles and gallons over several tanks for a steadier average.
Trip computers estimate fuel use from sensors and can differ from a hand calculation. Hand measurement based on the pump's gallons is usually a better check.
Enter the gallons added at the refill that ends your measurement period, since that is the fuel used over the miles you drove.
Not for a result in MPG. Convert to miles and US gallons first, or use the MPG to L/100km Converter to translate an MPG result.
Reference: EPA Fuel Economy