MPG Calculator — Miles Per Gallon Fuel Efficiency
Calculate your vehicle's fuel efficiency in MPG, L/100km, and cost per mile. See also Fuel Cost Calculator and Mileage Calculator.
How to Calculate MPG
1. Fill your tank completely and note the odometer reading (or reset trip meter). 2. Drive normally until you need to refuel. 3. Fill the tank again and note how many gallons it took. 4. Record the new odometer reading and subtract the old one to get miles driven. 5. Divide miles driven by gallons used to get your MPG.
MPG Formula
MPG = Miles Driven / Gallons Used
L/100km = 235.215 / MPG
km/L = MPG x 1.60934 / 3.78541
Cost per Mile = Fuel Price ($/gal) / MPG
Cost per 100 Miles = Cost per Mile x 100
Example
Drove 350 miles, used 12 gallons, gas at $3.50/gal:
MPG = 350 / 12 = 29.2 MPG
L/100km = 235.215 / 29.2 = 8.1
Cost per Mile = $3.50 / 29.2 = $0.120
Cost per 100 Miles = $12.00
MPG to L/100km Reference Table
| MPG | L/100km | km/L | Cost/Mile @$3.50 |
|---|---|---|---|
| 15 | 15.7 | 6.4 | $0.233 |
| 18 | 13.1 | 7.7 | $0.194 |
| 20 | 11.8 | 8.5 | $0.175 |
| 22 | 10.7 | 9.4 | $0.159 |
| 25 | 9.4 | 10.6 | $0.140 |
| 28 | 8.4 | 11.9 | $0.125 |
| 30 | 7.8 | 12.8 | $0.117 |
| 33 | 7.1 | 14.0 | $0.106 |
| 35 | 6.7 | 14.9 | $0.100 |
| 38 | 6.2 | 16.2 | $0.092 |
| 40 | 5.9 | 17.0 | $0.087 |
| 45 | 5.2 | 19.1 | $0.078 |
| 50 | 4.7 | 21.3 | $0.070 |
Frequently Asked Questions
What is MPG?
MPG stands for Miles Per Gallon. It measures how far a vehicle can travel on one gallon of fuel. Higher MPG means better fuel efficiency and lower fuel costs.
What is the difference between MPG and L/100km?
MPG measures distance per unit of fuel (higher is better). L/100km measures fuel per unit of distance (lower is better). They are inversely related: L/100km = 235.215 / MPG.
Why is my actual MPG lower than the EPA rating?
EPA ratings are measured under controlled conditions. Real-world MPG is affected by driving style, traffic, weather, terrain, tire pressure, and vehicle maintenance. Most drivers get 10-20% less than the EPA estimate.
Is city or highway MPG better?
Highway MPG is typically 20-30% better than city MPG because steady-speed driving is more efficient than stop-and-go traffic. Hybrids are an exception — they often get better city MPG due to regenerative braking.
How much can I save by improving MPG?
Improving from 20 to 25 MPG saves about $700/year at $3.50/gal driving 15,000 miles. Going from 25 to 30 MPG saves about $350/year. The savings are larger at lower MPG values.