Gas Mileage Calculator

About Gas Mileage Calculator

Calculate your vehicle's fuel efficiency in MPG, L/100km, and km/L. Estimate trip fuel costs for any distance, and compare two vehicles side by side to see the annual savings. Supports miles and kilometres, gallons and litres, and multiple currencies.

How to Calculate MPG

The formula is straightforward:

MPG = Miles Driven / Gallons Used

The most accurate way to measure your real-world fuel economy:

1. Fill your tank completely
2. Reset your trip odometer (or note the reading)
3. Drive normally until you need fuel again
4. Fill up again and note the gallons/litres added
5. Divide the miles driven by the fuel added

Example: You drove 312 miles and put in 10.4 gallons. MPG = 312 / 10.4 = 30.0 MPG.

For a more reliable number, do this over 3-4 fill-ups and average the results. Single-tank measurements can vary by 10-15% depending on driving conditions.

MPG vs L/100km vs km/L

Different countries use different fuel economy measures:

Measure	Used In	Better Economy Is	Conversion
MPG (US)	United States	Higher number	Baseline
MPG (Imperial)	United Kingdom	Higher number	1 imp. MPG = 1.201 US MPG
L/100km	Europe, Canada, Australia	Lower number	235.215 / US MPG
km/L	Japan, India, parts of Asia	Higher number	US MPG x 0.4251

Important: UK and US gallons are different sizes. A US gallon is 3.785 litres; a UK (Imperial) gallon is 4.546 litres. So a car rated at 30 US MPG would be rated at 36 Imperial MPG. This catches a lot of people out when comparing US and UK fuel economy figures.

Quick conversion: L/100km = 235.215 / US MPG. So 30 US MPG = 235.215 / 30 = 7.84 L/100km.

Average Fuel Economy by Vehicle Type

Vehicle Type	Typical MPG (US)	Typical L/100km
Small car (Corolla, Civic)	30-38	6.2-7.8
Midsize sedan (Camry, Accord)	28-34	6.9-8.4
Small SUV/Crossover	25-32	7.4-9.4
Large SUV (Tahoe, Explorer)	18-24	9.8-13.1
Pickup truck	15-22	10.7-15.7
Hybrid (Prius, Ioniq)	45-58	4.1-5.2
Plug-in hybrid (EV mode)	80-130 MPGe	1.8-2.9

The US EPA-rated average for new vehicles sold in 2024 was about 28.6 MPG combined. That number has roughly doubled since the 1970s, driven by fuel injection, aerodynamics, lighter materials, and hybrid technology.

Trip Cost Calculation

To estimate fuel cost for a trip:

Fuel Cost = (Distance / MPG) x Price per Gallon

Example: A 500-mile road trip in a car that gets 28 MPG, with fuel at $3.50/gallon:

Fuel needed = 500 / 28 = 17.86 gallons. Cost = 17.86 x $3.50 = $62.50.

For the same trip in a 17 MPG truck: 500 / 17 = 29.41 gallons x $3.50 = $102.94. That is $40.44 more in fuel alone.

What Affects Fuel Economy

Your real-world MPG can be significantly different from the manufacturer's rating. The biggest factors:

• Speed: Most vehicles are most efficient at 45-55 mph. According to the US Department of Energy, each 5 mph over 50 mph is roughly equivalent to paying an extra $0.24 per gallon (at $3.50/gal). At 80 mph, aerodynamic drag alone consumes about 40% of the engine's output.
• Driving style: Aggressive acceleration and hard braking can reduce MPG by 15-30% in city driving. Smooth, gradual speed changes save fuel and brakes.
• Temperature: Cold weather reduces fuel economy by 15-25% for short trips. The engine runs rich when cold, the battery is less efficient, and winter fuel blends have slightly less energy per gallon.
• Tyre pressure: Under-inflated tyres increase rolling resistance. Every 1 psi drop below recommended pressure reduces MPG by about 0.2%. Check monthly.
• Air conditioning: A/C can reduce MPG by 5-25% depending on conditions. At highway speeds, A/C is usually more efficient than open windows (which create drag).
• Payload: Extra weight costs fuel. Roughly 1-2% MPG reduction per 100 pounds of added weight. Clear out the boot/trunk if you are carrying unnecessary items.
• Terrain: Hilly routes use more fuel even though you recover some energy going downhill. Mountain driving can reduce efficiency by 10-20%.

Vehicle Comparison: Annual Savings

The comparison mode shows how much you would save per year by choosing a more efficient vehicle. The formula:

Annual Fuel Cost = (Annual Miles / MPG) x Fuel Price

Example: Comparing two vehicles over 12,000 miles per year at $3.50/gallon:

	SUV (22 MPG)	Hybrid (50 MPG)
Gallons per year	545	240
Annual fuel cost	$1,909	$840
5-year fuel cost	$9,545	$4,200

The hybrid saves $1,069 per year, or $5,345 over 5 years. That often offsets a higher purchase price, especially if fuel prices rise.

For detailed trip expense planning including fuel stops, try the fuel cost calculator. If you are financing a vehicle purchase, the auto loan calculator helps estimate monthly payments.

All calculations run in your browser. No data is stored or sent anywhere.