Gas Mileage Calculator
Estimate Gas Mileage by entering distance, fuel efficiency, and price per litre or gallon. See total fuel cost and CO₂ emissions for any journey.
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy
Gas Mileage Calculator Formula
MPG = Miles Driven ÷ Gallons Used
Divide the total miles driven by the gallons of fuel consumed to get miles per gallon (MPG). Cost per mile equals total fuel cost divided by miles driven. For the metric equivalent, convert to liters per 100 kilometers using: L/100km = 235.215 ÷ MPG. Annual cost is estimated based on 12,000 miles driven per year.
Gas Mileage Calculator — Worked Examples
Example 1: Daily Commute Efficiency
Problem:You drove 350 miles on 12 gallons of gas at $3.50/gallon. What is your fuel efficiency?
Solution:MPG = 350 / 12 = 29.2 MPG\nCost per mile = (12 × $3.50) / 350 = $0.120/mile\nL/100km = 235.215 / 29.2 = 8.1 L/100km\nAnnual cost (12k mi) = (12,000 / 29.2) × $3.50 = $1,438
Result:29.2 MPG | $0.120/mile | 8.1 L/100km | $1,438/year
Example 2: Road Trip Calculation
Problem:A 600-mile road trip used 20 gallons at $3.80/gallon.
Solution:MPG = 600 / 20 = 30.0 MPG\nCost per mile = (20 × $3.80) / 600 = $0.127/mile\nTotal trip cost = 20 × $3.80 = $76.00\nL/100km = 235.215 / 30 = 7.8 L/100km
Result:30.0 MPG | $0.127/mile | Trip cost: $76.00
Gas Mileage Calculator — Frequently Asked Questions
How can I improve my car's gas mileage?
Several driving habits and maintenance practices can improve fuel economy by 10-30%. Drive at moderate speeds — fuel efficiency drops significantly above 50 mph (each 5 mph over 50 is like paying an extra $0.20-0.30 per gallon). Avoid aggressive acceleration and hard braking; use cruise control on highways. Keep tires properly inflated (under-inflation by 1 psi reduces efficiency by 0.2%). Remove excess weight and roof cargo carriers when not in use. Keep up with maintenance: clean air filters, fresh spark plugs, and proper oil improve efficiency. Use the recommended octane fuel — premium does not help if your car does not require it.
How much does driving speed affect gas mileage?
Speed has a dramatic effect on fuel economy due to aerodynamic drag, which increases with the square of velocity. Most cars achieve peak fuel efficiency between 35-55 mph. Above 55 mph, efficiency drops rapidly: driving at 65 mph uses about 8% more fuel than 55 mph, 75 mph uses about 20% more, and 85 mph uses about 35% more. In practical terms, slowing from 75 to 65 mph on a highway trip can save about 15% on fuel. City driving is less efficient than highway due to frequent stops, idling, and acceleration, which is why hybrid vehicles excel in city conditions with regenerative braking.