MPG Calculator

By AutoFixr Editorial Team · Updated November 11, 2026

How to Calculate MPG

MPG stands for miles per gallon. It tells you how far your car travels on one gallon of fuel, and it is the standard fuel economy number in the United States. The formula is: MPG equals miles divided by gallons. Drive 300 miles on 10 gallons and your MPG is 30. Drive 250 miles on 12.5 gallons and your MPG is 20.

The most accurate way to measure it is the full tank method. Fill the tank until the pump clicks off, then reset the trip meter to zero or write down the odometer reading. Drive normally for a few days, then fill up again to the same click off point. The gallons on the pump receipt are the fuel you used. Divide the trip miles by those gallons and you have your MPG. One fill-up gives a useful number, but three or four tanks averaged together give a better one, because traffic and weather can move a single tank by several MPG.

What Is a Good MPG?

A good MPG depends on the kind of car you drive. A typical gasoline car in the US gets about 25 MPG combined, which blends city and highway driving. Small cars do better, trucks do worse, and hybrids beat them all. The table below shows typical combined MPG ranges by vehicle class. These are broad ranges for illustration, not ratings for a specific model. For the exact rating on your car, check fueleconomy.gov, the official site run by the US Department of Energy and the EPA.

Cost per 1,000 miles turns MPG into dollars. At $3.50 per gallon, a 30 MPG car costs about $117 in fuel per 1,000 miles, while a 20 MPG truck costs $175 for the same distance. Over 12,000 miles a year, that gap is about $700. A small MPG gain also matters more at the low end: going from 15 to 20 MPG saves more fuel than going from 35 to 40 MPG. Do not compare your car to a different class. A pickup at 20 MPG can be a fine result, while a compact car at 20 MPG would be a warning sign.

MPG to L/100 km Conversion Table

Most of the world measures fuel economy in liters per 100 kilometers, written as L/100 km. The two scales run in opposite directions: higher MPG is better, but lower L/100 km is better. To convert, divide 235.215 by the US MPG figure. The calculator shows all three conversions at once.

The UK gallon is larger than the US gallon, about 4.546 liters versus 3.785 liters, so the same car shows about 20 percent more MPG in UK figures. Multiply US MPG by 1.201 to get UK MPG.

How to Use the Trip Cost Mode

Knowing your MPG is only half the job. The trip cost mode turns it into a budget. Enter the trip distance, your MPG, and the price per gallon, and the calculator shows the fuel you will need and what it will cost. A 300 mile trip at 30 MPG uses 10 gallons, and at $3.50 a gallon that is $35.00. Turn on the round trip switch and the distance doubles to 600 miles and the cost doubles to $70.00. If four people are sharing the drive, enter 4 in the people box and the cost splits to $17.50 each.

The trip mode also shows cost per mile, which is the most useful number for comparing trips and cars. Divide the price per gallon by your MPG to get it: $3.50 divided by 30 MPG is about $0.117 per mile. A 20 MPG truck at the same price costs $0.175 per mile, so every mile costs about 6 cents more. The yearly fuel cost line uses the miles you drive per year, set to 12,000 miles by default. The CO2 figure uses the EPA factor of 8.887 kilograms per gallon, and the optional EV comparison shows the same trip in charging cost.

Why Your MPG Is Lower Than the EPA Rating

Almost every driver gets less than the EPA combined rating, and that is normal. The EPA tests cars in a laboratory on a set drive cycle, with no traffic, no hills, no air conditioning load and a warmed up engine. Real life adds all of those back. Short trips are the worst case, because a cold engine runs rich and burns extra fuel until it warms up, and a two mile trip may never get warm at all. Cold weather makes it worse: cold air is denser, tires lose pressure, winter fuel blends carry slightly less energy, and heaters draw power.

Speed matters more than most drivers expect. Fuel economy is usually best at a steady 50 to 60 mph on the highway. Above 60 mph, aerodynamic drag rises fast, and every 5 mph over 50 mph is like paying extra for each gallon. Aggressive driving costs even more: hard acceleration, hard braking and speeding can cut highway MPG by up to 30 percent, according to the US Department of Energy. Underinflated tires are the most common mechanical cause, and the Department of Energy notes that correct tire pressure can improve MPG by up to 3 percent. A check engine light should never be ignored either: a faulty oxygen sensor or a misfire can waste fuel before the car feels any different.

How to Improve Your MPG

Start with the free fixes. Drive smoothly, look ahead, and lift off the gas early instead of braking late. Keep a steady speed on the highway and use cruise control on flat roads. Avoid idling for more than a minute, since a modern engine uses less fuel restarting than idling for long. Remove roof racks when you are not using them, take heavy items out of the trunk, and combine short errands into one trip so the engine warms up once instead of three times.

Next, check the maintenance items that affect fuel use. Keep tires inflated to the pressure on the door jamb placard, not the maximum pressure on the tire sidewall, and check them monthly when the tires are cold. Change the engine oil on schedule and use the grade in the owner manual, since thicker oil than specified adds drag inside the engine. Replace the engine air filter when it is dirty, and replace spark plugs at the interval in the manual. Fuel additives rarely deliver anything measurable, and premium gasoline does not help a car designed for regular unleaded.

Frequently Asked Questions

Reviewed by the AutoFixr Editorial Team. Every fact in this guide was checked against US Department of Energy, EPA and fueleconomy.gov guidance. Fuel prices change weekly, so enter the current price at the pump or from the EIA. MPG figures vary by vehicle, load and driving conditions. Always follow your owner manual.