Gas Mileage Calculator (MPG)
Calculate your vehicle's fuel efficiency in MPG, L/100km, and km/L. Estimate fuel costs per mile and plan trip expenses based on distance and gas prices.
How to Calculate Gas Mileage
Gas mileage (fuel efficiency) measures how far your vehicle travels on a given amount of fuel. In the US, it is expressed as miles per gallon (MPG). Most other countries use liters per 100 kilometers (L/100km) or kilometers per liter (km/L). To calculate your MPG, fill your tank completely, reset your trip odometer, drive normally until you need fuel again, then divide the miles driven by the gallons used to refill.
Fuel Efficiency Formulas
MPG = Miles Driven / Gallons Used
L/100km = (Liters Used / Kilometers Driven) x 100
km/L = Kilometers Driven / Liters Used
MPG to L/100km: L/100km = 235.215 / MPG
Cost per Mile = Fuel Price per Gallon / MPG
Trip Cost = (Distance / MPG) x Price per Gallon
MPG vs L/100km
MPG and L/100km have an inverse relationship — higher MPG means lower L/100km. The US, UK, and a few other countries use MPG, while most of the world uses L/100km. Note that US gallons (3.785 liters) are smaller than Imperial gallons (4.546 liters), so UK MPG figures are about 20% higher than US MPG for the same vehicle. This calculator uses US gallons.
Tips to Improve Fuel Efficiency
Maintain proper tire pressure: Under-inflated tires increase rolling resistance and can reduce MPG by 3%.
Drive at moderate speeds: Fuel efficiency drops significantly above 50 mph. Each 5 mph over 50 costs roughly $0.20 more per gallon.
Avoid aggressive driving: Rapid acceleration and hard braking can lower MPG by 15-30% on highways.
Remove excess weight: Every 100 pounds of extra weight reduces MPG by about 1%.
Use cruise control: Maintaining a constant speed on highways improves efficiency by 7-14%.
Keep up with maintenance: A well-tuned engine, clean air filter, and fresh oil all contribute to better fuel economy.
Average MPG by Vehicle Type
| Vehicle Type | City MPG | Highway MPG | Combined MPG | L/100km |
|---|---|---|---|---|
| Compact Car | 28-32 | 36-42 | 31-36 | 6.5-7.6 |
| Midsize Sedan | 25-30 | 34-40 | 29-34 | 6.9-8.1 |
| Full-size Sedan | 22-27 | 30-36 | 25-30 | 7.8-9.4 |
| Small SUV/Crossover | 24-28 | 30-35 | 26-31 | 7.6-9.0 |
| Midsize SUV | 20-25 | 26-32 | 22-28 | 8.4-10.7 |
| Full-size SUV | 15-20 | 20-26 | 17-22 | 10.7-13.8 |
| Pickup Truck | 16-20 | 21-26 | 18-22 | 10.7-13.1 |
| Hybrid | 45-55 | 45-50 | 45-52 | 4.5-5.2 |
| Plug-in Hybrid | 80-100* | 35-40 | 55-70 | 3.4-4.3 |
| EV (MPGe) | 100-140* | 90-120* | 95-130* | 1.8-2.5* |
* EV and plug-in hybrid figures use MPGe (miles per gallon equivalent) for electric-only driving.
Frequently Asked Questions
How do I calculate my car's MPG accurately?
Fill your tank completely, note the odometer reading (or reset the trip meter), drive normally for at least one full tank, then fill up again. Divide the miles driven by the gallons used to refill. Repeat over several tanks for a reliable average.
Why is my actual MPG lower than the EPA rating?
EPA ratings are measured under controlled laboratory conditions. Real-world factors like aggressive driving, cold weather, short trips, heavy loads, roof racks, and city traffic all reduce actual fuel economy. Most drivers get 10-20% less than the EPA combined rating.
What is the difference between US and Imperial gallons?
A US gallon is 3.785 liters while an Imperial (UK) gallon is 4.546 liters — about 20% larger. This means UK MPG figures are higher than US MPG for the same vehicle. This calculator uses US gallons.
How do I convert MPG to L/100km?
Divide 235.215 by the MPG value. For example, 30 MPG = 235.215 / 30 = 7.84 L/100km. The relationship is inverse — higher MPG means lower L/100km.
Does AC affect gas mileage?
Yes. Air conditioning can reduce fuel economy by 5-25% depending on conditions. At low speeds, opening windows is more efficient. At highway speeds (above 45 mph), AC is more efficient than open windows due to aerodynamic drag.
What is a good MPG for a car?
For a non-hybrid gasoline car, 30+ MPG combined is considered good, 35+ is very good, and 40+ is excellent. Hybrids typically achieve 45-55 MPG. The average new car in the US gets about 26 MPG combined.
How much can I save by improving my MPG?
If you drive 12,000 miles per year at $3.50/gallon, improving from 25 MPG to 30 MPG saves about $280/year. Going from 20 to 30 MPG saves $700/year. The savings are larger when starting from lower MPG values due to the inverse relationship.