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5 Min. Read

How to Calculate Gas Mileage in the Right Way

How to Calculate Gas Mileage in the Right Way

As a small business owner, it’s critical your vehicle be as efficient as it can be. While fuel costs can be written off if you use your car for your business, it’s always better to simply save the money upfront.

However, not many people know how to calculate gas mileage correctly. How do you know how much fuel has been used, and then compare that to how many miles you have driven?

Fortunately, it doesn’t have to be difficult. You can use online gas mileage calculators or you can figure it out yourself using the calculator on your phone.

Here’s what you need to know!

Here’s What We’ll Cover:

Why Does Gas Mileage Matter?

How to Calculate Gas Mileage

Factors That Impact Gas Mileage

Calculate Your Gas Mileage Accurately

Why Does Gas Mileage Matter?

Why is it important to know the gas mileage for your car? Knowing how efficient your vehicle is helps you in several ways.

First, it can help you determine how much you’re likely to spend on gas for business purposes. If you use your car for business, you need to be able to forecast how much you’ll need to spend on a variety of things, including fuel. This is a variable cost and can be difficult to determine if you don’t know your gas mileage.

Second, you can’t write off all the maintenance and costs of your vehicle on your taxes. Instead, you only need to count the portion that’s for business. The IRS allows you to use a standard write-off for business use, which is $0.56/mile for 2021. If you want to be more precise, you can figure out the specific cost of fuel. This means determining your gas mileage and multiplying that by the number of miles you drive for business.

Finally, knowing your current gas mileage can help you determine if a new car is a good investment for your business. Comparing the new car’s miles per gallon with your current car will help you determine part of the return on your investment.

Of course, it always helps to get better fuel prices, no matter what your mileage is. That’s where an app like GasBuddy can make a big difference.

How to Calculate Gas Mileage

So how do you find the number you’re looking for when it comes to gas mileage? Here’s the right way to calculate it. 

You’ll start when you fill up your gas tank. Make sure you fill it all the way, not partially. Then, either write down the odometer reading or set the trip odometer to zero.

From there, you’ll drive like you normally would. If you use the car only for business, there’s no additional record-keeping. If you use the car for personal use and your company, you’ll want to write down how many miles you drive for business.

The next time you fill up your car with gas, fill it up all the way again. Note how many gallons it takes — that’s how many gallons of gas you used. Then take a look at how many miles you’ve driven. Divide the miles by the gallons, and you’ve got how many miles per gallon you get. That’s your gas mileage!

If you have a specific number of miles you’ve driven for business, you can then multiply your gas mileage by the number of business miles. This will give you the business-specific fuel cost for that timeframe.

It’s important to figure your miles per gallon several times, preferably throughout the year. There are a lot of variables that impact the number, and when you find it multiple times, you’ll get a good average gas mileage.

Factors That Impact Gas Mileage

You might think that your car will always get the same miles per gallon, but actually that isn’t true. Different road conditions and other factors can dramatically impact your gas mileage. Here are a few to keep in mind.

The Type of Driving. If you make a lot of short trips during one of your measurement periods, you’ll get a lower miles-per-gallon than if you did a lot of long-distance driving. Starting and stopping the engine uses a lot of fuel.

Wind Resistance. Any type of air drag will decrease the efficiency of your vehicle. That means driving with your windows down on a nice day can make your car less fuel-efficient. Having a roof rack or ski rack creates drag as well. Sometimes it’s worth it, but keep in mind your gas mileage will be affected.

Inefficient Speeds. The best speed for fuel economy is between 40 — 55 mph. Once you start going faster than 60, fuel economy will drop. Because most highways have a speed limit of 65+, that means that highway driving can be less fuel-efficient than driving on other types of roads.

Extra Weight in the Car. Everyone keeps a spare tire in the trunk, but if you also carry a lot of heavy equipment, you’ll get a lower gas mileage than a vehicle without the extra weight. 

Calculate Your Gas Mileage Accurately

Knowing your specific gas mileage can help you make more fuel-efficient decisions. It can also determine your fuel usage for taxes and help you decide if a new car is worthwhile. Knowing how to accurately calculate mileage can make a big difference in the longevity of your vehicle and in your bank account at the end of the month.


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