What is the difference between MPG and L/100km?

MPG (miles per gallon) measures how far you travel per unit of fuel — higher is better. L/100km (liters per 100 kilometers) measures how much fuel you consume per unit of distance — lower is better. To convert: L/100km = 235.21 ÷ MPG (US).

How accurate is the gas mileage calculation?

The calculation is mathematically exact given your inputs. Real-world accuracy depends on how precisely you measure distance (odometer or GPS) and fuel (pump display). For best results, fill your tank to the same level each time and use the exact pump reading.

What does cost per mile mean?

Cost per mile is the total fuel cost divided by miles driven. For example, at 30 MPG with gas at $3.50/gallon, your fuel cost is $3.50 ÷ 30 = $0.117 per mile. Multiply by your annual mileage to get your yearly fuel bill.

Which gallon does this calculator use?

This tool uses US gallons (3.785 L) for Imperial mode. Metric mode uses liters, which avoids gallon ambiguity entirely. To convert US MPG to UK MPG, multiply by 1.201.

How do I use the vehicle comparison feature?

Switch to the Compare tab, enter the efficiency values for both vehicles, your fuel price, and annual mileage. The tool calculates annual fuel cost for each vehicle and shows you the yearly and 5-year savings of the more efficient option.

How much does gas cost per mile?

Divide the price per gallon by your MPG. At $3.50 a gallon, a 25 MPG car costs $0.140 a mile and a 40 MPG car $0.087, so 12,000 miles a year costs $1,680 against $1,050.

Why is my MPG lower than the EPA rating?

EPA ratings come from standard lab tests. Short trips, cold weather, speeds above about 50 mph, roof racks and underinflated tires all lower real-world mileage.

Gas Mileage Calculator

Enter distance and fuel used to get MPG or L/100km, cost per mile, and compare two vehicles side by side.

Gas mileage = miles driven ÷ gallons used.

Unit System

Distance Traveled

Fuel Consumed

gal

Fuel Price (optional)

$/gal

Annual Mileage (optional)

mi/yr

Enter distance and fuel used, then click Calculate.

Fuel Efficiency (MPG)

Shared Settings

Fuel Price ($/gal)

Annual Mileage (mi)

Comparison Results

Metric	Vehicle A	Vehicle B
Fuel Efficiency	—	—
Annual Fuel Cost	—	—
Cost Per Mile	—	—
Annual Gallons	—	—

Quick answer

Gas mileage = miles driven ÷ gallons used. 300 miles on 10 gallons is 30 MPG, or 7.84 L/100 km. Fill the tank, reset the trip meter, drive as usual, then fill up again and divide the miles by the gallons it took. Add the gas price to see your cost per mile.

Examples

Miles driven	Gallons used	MPG	L/100 km
300	10	30.0	7.84
350	12.5	28.0	8.40
412	13.2	31.2	7.54
250	11	22.7	10.35

Enter miles driven and gallons used.

Summary

The Gas Mileage Calculator converts any distance-and-fuel pair into MPG or L/100km instantly. Enter a fuel price and annual mileage to see your cost per mile and projected yearly fuel spend. Use the comparison panel to put two vehicles side by side and find out exactly how much you could save by switching to a more efficient car.

How it works

Choose US customary (miles + US gallons) or Metric (km + liters) units.
Enter the distance you drove and the fuel you consumed.
Your fuel efficiency — MPG or L/100km — appears immediately.
Add a fuel price and annual mileage to see cost-per-mile and yearly spend.
Open the Compare tab to enter a second vehicle and calculate annual savings.

Use cases

Verify your car's real-world fuel economy after a road trip.
Decide whether a more efficient new car will pay for itself.
Estimate annual fuel costs before buying or leasing a vehicle.
Convert between MPG and L/100km for international comparisons.
Monitor fleet vehicles for unexpected fuel consumption increases.
Calculate cost savings from carpooling or route optimization.
Compare a gasoline car against a hybrid for the same commute.
Plan a cross-country trip budget based on actual measured efficiency.

Frequently Asked Questions

Last updated: 2026-05-29 · Reviewed by Nham Vu