Gas Mileage Calculator

What this calculator does

The Gas Mileage Calculator measures how far a vehicle traveled on a known amount of fuel. You enter the current odometer reading, the previous reading, and the fuel added at the last fill-up. The calculator returns the distance traveled, miles per gallon, liters per 100 kilometers, and kilometers per liter.

You can work in US units or metric units. An optional fuel price adds the fill-up expense, the cost per mile or kilometer, and the distance you can drive per dollar. Leaving the price blank keeps the result focused on efficiency.

How to use this calculator

1. Choose US units or metric units.
2. Enter the current odometer reading.
3. Enter the previous odometer reading, taken at the prior fill-up.
4. Enter the fuel added to the tank.
5. Optionally enter the fuel price.
6. Click Calculate.

For the most consistent result, fill the tank to the same level each time. The method works best when the fuel added represents all the fuel used since the previous reading.

Formula

Distance traveled = current odometer - previous odometer
Miles per gallon = distance (miles) / fuel added (gallons)
Liters per 100 km = 235.214583 / mpg
Kilometers per liter = distance (km) / fuel added (liters)

In metric mode, the distance is already in kilometers and the fuel is in liters. The calculator converts those values to miles and gallons internally so it can report mpg as well. One mile equals 1.609344 kilometers and one US gallon equals 3.785411784 liters.

When a price is entered, the fill-up expense is the fuel added multiplied by the price. Cost per mile is the expense divided by the distance, and miles per dollar is the distance divided by the expense.

Default example

With a current reading of 12,360 miles, a previous reading of 12,000 miles, 15 gallons added, and $3.00 per gallon, the vehicle traveled 360 miles and returned 24 mpg. That equals about 9.8 L/100 km and 10.2 km/L. The fill-up cost is $45.00, the cost is $0.125 per mile, and the vehicle travels 8 miles per dollar.

The metric example uses 18,900 km and 18,300 km with 50 liters at $1.00 per liter. The distance is 600 km, efficiency is 12 km/L or about 8.3 L/100 km, and the fill-up costs $50.00.

Assumptions and limitations

• The odometer difference must be positive; the current reading has to be greater than the previous reading.
• A single fill-up gives a short-term estimate. Several tank-to-tank measurements averaged together are more reliable.
• Fuel added is assumed to equal fuel burned since the previous fill-up.
• Tire size, odometer calibration, roof cargo, idling, and driving conditions can change real efficiency.
• The result uses the US gallon. Imperial gallons would produce different mpg figures.

Frequently asked questions

Why does my result differ from the EPA rating?

The EPA rating is a laboratory-based estimate intended for vehicle comparisons. Your result reflects your own route, speed, weather, load, and driving style. Short trips and cold starts often produce noticeably lower mileage.

How many fill-ups should I average?

Three to five tank-to-tank measurements usually give a stable picture. Keep filling to the same level and record every odometer reading. A single measurement can be distorted by a partial fill or a long highway trip.

What happens if I leave the gas price blank?

The efficiency results still calculate normally. Only the expense, cost-per-distance, and distance-per-dollar rows are omitted. Enter a price if you want the full cost breakdown.

Reference table

Odometer reading examples

Record the odometer at each fill-up and divide the distance by the fuel added.

Source

Reference: Calculator.net - Gas Mileage Calculator. Unit conversion factors follow the international mile and the US liquid gallon.