Gas Mileage Calculator
Find miles per gallon, liters per 100 km, and trip cost from distance, fuel used, and price.
What it does
Fuel economy tells you how far a vehicle travels on a given amount of fuel. It is the main number drivers use to compare cars and to estimate travel costs.
The tool above turns distance, fuel used, and price into miles per gallon, liters per 100 km, and the total trip cost. Enter your trip numbers and read the result.
MPG and liters per 100 km measure the same thing in opposite directions: higher MPG means better economy, while lower liters per 100 km means better economy.
Fuel price turns efficiency into dollars, so you can see what a trip costs before you drive it. Real economy varies with speed, load, traffic, and weather, so treat this as an estimate.
How to use
- Enter the distance driven.
- Enter the fuel used for that distance.
- Enter the fuel price per gallon.
- Pick miles or kilometers and gallons or liters.
- Read MPG first, then liters per 100 km and trip cost.
Formula
- distance
- Distance driven in miles or kilometers.
- gallons
- Fuel used in gallons or liters.
- price
- Fuel price per gallon in dollars.
- MPG
- Miles per gallon, miles driven per gallon of fuel.
The 235.214583 factor converts between MPG and liters per 100 km using the US gallon and kilometer definitions. Metric distance converts at 1.609344 km per mile, and metric fuel at 3.78541 liters per gallon.
Worked example
Example: 300 miles on 10 gallons at $3.50 per gallon
Distance 300 miles, fuel used 10 gallons, price $3.50 per gallon, imperial units.
- MPG: 300 miles / 10 gallons = 30 mpg.
- Liters per 100 km: 235.214583 / 30 = 7.84 L/100km.
- Trip cost: 10 gallons x $3.50 = $35.00.
- Metric: 300 miles is 482.8 km and 10 gallons is 37.85 liters.
- Tool shows 30 mpg, 7.84 L/100km, and $35.00 trip cost.
Reference table
| Distance | MPG | L/100km | Trip cost |
|---|---|---|---|
| 200 mi | 20 mpg | 11.76 L/100km | $35.00 |
| 300 mi | 30 mpg | 7.84 L/100km | $35.00 |
| 400 mi | 40 mpg | 5.88 L/100km | $35.00 |
| 500 mi | 50 mpg | 4.70 L/100km | $35.00 |
Limits
- Real fuel economy varies with speed, load, traffic, terrain, and weather.
- The tool assumes the same fuel type and price for the whole trip.
- MPG and liters per 100 km are not interchangeable in casual conversation without converting.
- Diesel, electric, and hybrid vehicles use different measures.
Common mistakes
- Confusing higher liters per 100 km with better economy, when lower is better.
- Mixing miles and liters without converting units first.
- Using pump price instead of the actual price paid per gallon.
- Forgetting that ethanol blends and winter fuel can lower MPG.
- Comparing MPG across vehicle classes with different loads.
Try it yourself
Quick checks. Answers sit tucked under each question.
240 mi on 8 gal?
30 mpg, 7.84 L/100km, trip cost $28.00 at $3.50 per gallon.
360 mi on 12 gal at $4.00?
30 mpg, 7.84 L/100km, trip cost $48.00.
150 mi on 5 gal?
30 mpg, 7.84 L/100km, trip cost $17.50 at $3.50 per gallon.
Questions
What is MPG?
Miles per gallon: how many miles a vehicle travels on one gallon of fuel.
How does L/100 km differ from MPG?
L/100 km is liters used per 100 kilometers. Lower is better; MPG higher is better.
Is 30 mpg good?
It is reasonable for many cars; hybrids and small cars do better, trucks and SUVs often do worse.
Does speed change MPG?
Yes. Higher highway speeds usually lower fuel economy.
Can I use liters and kilometers?
Yes. The tool converts metric inputs to MPG and L/100 km automatically.
Is trip cost exact?
No. It is an estimate based on the price and fuel you enter; real prices and economy vary.