Fuel Cost Calculator finds the fuel needed and its total cost from distance, fuel economy, and fuel price, then adds cost per mile, a 10% price change, and savings at a higher MPG.
How the Fuel Cost Calculator Works Out Fuel Spend
The Fuel Cost Calculator turns a distance, a fuel economy rating and a fuel price into the fuel your vehicle burns and what that fuel costs. Drivers use it to price a commute, budget monthly fuel, or see what a more efficient car would save.
Enter the distance in miles or kilometers. Enter fuel economy as MPG (US), MPG (UK), L/100 km or km/L. Then enter the fuel price per US gallon, liter or UK gallon.
The main result shows the total fuel cost for that distance. The cards below show the fuel needed, the cost per mile, the effect of a price change, and the cost at a second fuel economy you want to compare.
The Fuel Cost Calculator Formula
The math takes two steps. First, find how much fuel the distance needs.
$$\text{Fuel needed} = \frac{\text{Distance}}{\text{Fuel economy}}$$
Then multiply that fuel by the price of one unit of fuel.
$$\text{Fuel cost} = \text{Fuel needed} \times \text{Fuel price}$$
With the default inputs, 300 miles at 25 MPG needs 12 gallons. At $3.50 a gallon, that fuel costs $42.00. It works out to $0.14 per mile, or $14.00 per 100 miles.
When fuel economy is entered as L/100 km, the tool flips the first step. It multiplies the distance by the consumption figure instead of dividing, since L/100 km already states fuel used per distance.
A common mistake is entering the highway MPG from the window sticker when most of your driving is in town. The EPA label also lists a combined figure, and that one is the better match for mixed driving. Your own average from a few tanks is better still.
US Gallons, UK Gallons and Liters
Inside the tool, every input converts to kilometers and liters before the math runs. It uses exact definitions for each unit.
A US gallon is 231 cubic inches, which is exactly 3.785411784 liters under NIST Handbook 44. A UK imperial gallon is 4.54609 liters. A mile is exactly 1.609344 kilometers.
Because the UK gallon is about 20% larger, the same car posts a higher MPG number in Britain. A rating of 40 MPG (UK) equals about 33.3 MPG (US). Enter a UK figure as US MPG and the calculator will understate your fuel cost by about 17%.
The first result card of the Fuel Cost Calculator shows the fuel needed in the unit your price uses, plus the other two volume units. At the defaults, 12 US gallons equals 45.42 liters or 9.99 UK gallons.
For metric drivers who only know distance driven and liters used, the liter to km calculator gives you a km/L rating to enter here.
Why MPG Gains Aren’t Equal
The last card prices the same distance at a second fuel economy. With the defaults, moving from 25 to 35 MPG cuts the fuel from 12 gallons to 8.57 and saves $12.00.
That saving does not grow in a straight line with MPG. Fuel used per mile is the inverse of MPG, so each extra MPG saves less fuel than the one before it.
Duke University researchers Richard Larrick and Jack Soll called this the MPG illusion in a 2008 paper in Science. Their finding helped put a gallons per 100 miles figure on the EPA fuel economy label.
Here is how it plays out over 300 miles. Going from 15 to 20 MPG saves 5 gallons. Going from 30 to 40 MPG, a bigger jump on paper, saves only 2.5 gallons.
So when a household has two cars, upgrading the thirstier one usually saves more money. Run both options through the Fuel Cost Calculator comparison field to see it in dollars.
| Fuel economy | Gallons per 100 miles | L/100 km | Cost per 100 miles at $3.50 |
|---|---|---|---|
| 15 MPG | 6.67 | 15.7 | $23.33 |
| 20 MPG | 5.00 | 11.8 | $17.50 |
| 25 MPG | 4.00 | 9.4 | $14.00 |
| 30 MPG | 3.33 | 7.8 | $11.67 |
| 40 MPG | 2.50 | 5.9 | $8.75 |
| 50 MPG | 2.00 | 4.7 | $7.00 |
For reference, the EPA Automotive Trends Report puts the average model year 2024 new vehicle at a record 27.2 MPG. Without battery electric and plug-in hybrid models, the average drops by 1.7 MPG.
What a 10% Price Swing Does
The third card of the Fuel Cost Calculator shows your fuel cost if the pump price rises or falls by 10%. At the defaults, the $42.00 cost becomes $46.20 at $3.85 a gallon and $37.80 at $3.15.
Price moves hit your cost in a straight line. A 10% higher price always means a 10% higher fuel bill, unlike MPG changes.
This card helps when you budget ahead, since prices vary by state and change week to week. AAA listed the national average for regular at $4.475 on September 22, 2026. At that price, the same 300 miles costs $53.70.
Pump prices follow crude oil with a lag. The oil to gas price calculator shows how a change in the barrel price can reach the pump.
Where the Math Breaks Down
Distance, fuel economy and the comparison economy must all be greater than zero. The Fuel Cost Calculator stops and flags the field if any of them is zero or blank, since dividing by zero fuel economy has no meaning.
Fuel price can be zero. The tool then shows $0.00, which is only useful for checking fuel volume.
Realistic entries for light vehicles run from about 10 to 60 MPG (US). Very low figures, such as a heavy truck towing, produce large but valid costs. The alert box flags anything at 14 L/100 km or more, about 16.8 MPG (US), as high fuel use.
The currency menu only changes the symbol. It does not convert exchange rates, so enter the price in the currency you pay.
The estimate also leaves out time spent idling, which burns fuel without adding miles. The idling fuel consumption calculator covers that separately.
Mistakes That Skew the Estimate
Entering one-way distance when you drive there and back cuts the cost in half. Double the distance to cover both directions.
Leaving the price unit on gallons while typing a per-liter price makes fuel look almost four times cheaper than it is. Set the price menu to match the sign at the pump.
Entering the comparison car in a different unit than your own car gives a false saving. Both fields share the unit you pick in the fuel economy menu.
Fuel Cost Questions Drivers Ask
How do I calculate fuel cost for a set distance?
Divide the miles by your car’s MPG to get gallons, then multiply by the price per gallon. The Fuel Cost Calculator does both steps once you enter the distance. For 1,000 miles at 28 MPG, you need about 35.7 gallons. At $4.00 a gallon, that is about $142.86. Use your real-world MPG, and price the fuel at what you actually pay, since prices in some states run well above the national average.
Should I use the EPA rating or my own MPG in a fuel cost calculator?
Use your own MPG when you have it. EPA ratings come from standard lab test cycles, so your results can differ with speed, load, weather and terrain. To find yours, fill the tank and note the odometer. At the next fill, divide the miles driven by the gallons you added. Average two or three tanks. If you don’t have that data, use the EPA combined figure rather than the highway number.
How much does my commute cost in fuel each month?
Enter your daily commute distance, both ways, times your workdays per month. A 40-mile daily commute over 21 workdays is 840 miles. At 25 MPG and $3.50 a gallon, that costs $117.60 a month. The gas cost per month calculator breaks the same spend into daily, weekly and yearly figures. If you’re not sure of your yearly total, the miles per year calculator builds it from your habits.
How do I split fuel cost with passengers?
Divide the total fuel cost by the number of people sharing the ride. The default $42.00 split four ways is $10.50 each. Extra passengers and luggage do lower MPG a little, so a full car may burn slightly more than your usual figure. Keep in mind that fuel is only part of what driving costs, since tires, oil and wear also add up per mile.
Can I compare a gas car with an electric car?
Not directly, since the Fuel Cost Calculator works in liquid fuel units. Price the gas car here first. Then use the miles per kWh calculator to find the charging cost for the same distance, and compare the two totals. Make sure both use the same distance and a realistic local price for gas and electricity.