How to Calculate Estimated Miles per Gallon & Fuel Costs

Driving and fuel costs are a major concern for many Americans. With the rise in gas prices, many Americans are having to really budget their expenses and find out exactly how much their fuel costs might be in the upcoming months. Through some simple calculations, you too can find out estimated miles per gallon and fuel costs for your next trip or weekly commute.

Look in your vehicle owner's manual to find out how many gallons of gas your car's tank holds.

Write down your car's odometer reading when you fill up your tank with gas. Write down the new odometer reading once your gas tank hits "Empty" and you fill up the tank again.

Subtract the larger odometer reading from the smaller reading. Divide that number by the number of gallons in your gas tank. This gives you the estimated miles per gallon used by your car.

Note the current price of gas at your gas station to help calculate approximate fuel costs.

Calculate the number of miles in your next trip, from point A to point B. Divide that number by the miles per gallon to find out how many gallons of gas will be needed to complete the trip. Next, multiply the current price per gallon by the number of gallons needed to find total fuel costs.


  • Miles per gallon vary based on the miles per hour driven (which is why cars list highway and city mileage on the price sticker). Calculate miles per gallon over several tanks of gas to get a good average for your car. Your miles per gallon should increase over highway miles and decrease with city (or stop and go) driving.


  • Fuel costs vary, sometimes daily, due to oil prices. The fuel costs that you calculate one day may or may not be the same the next day. Use this as an approximation to help with budgeting.