MPG Calculator
Work out your real fuel economy in MPG, L/100km, and km/L, plus the cost per mile.
⛽ What is the MPG Calculator?
The MPG calculator measures your vehicle's fuel economy from two simple numbers: how far you drove and how much fuel you used. It returns miles per gallon, along with litres per 100 km and km per litre, so you can read your economy in whichever system you are used to. Add a fuel price and it also shows the cost per mile and per kilometre.
Drivers use it to check real-world efficiency rather than relying on the manufacturer's sticker figure, which comes from a lab test and is almost always optimistic. Measuring economy tank by tank reveals how your actual driving, traffic, and terrain affect running costs. It is also handy for budgeting a road trip, comparing two vehicles, spotting a maintenance problem when economy suddenly drops, and settling the perennial question of what a journey really costs in fuel.
The most important detail is the unit of gallon. A US gallon is 3.785 litres while a UK gallon is 4.546 litres, so the same car appears roughly 20 percent more efficient in UK MPG than in US MPG. This calculator reports US MPG. Another common confusion is that MPG and litres per 100 km run in opposite directions: a higher MPG is better, but a lower litres-per-100-km figure is better, because one measures distance per fuel and the other measures fuel per distance.
This tool is useful because it does the arithmetic and the unit conversions in one step, turning a distance and a fuel amount into a clear picture of efficiency and cost, with the working shown so you can see exactly how the numbers connect.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - 300 miles on 12 gallons at 3.50
Example 2 - 500 km on 40 litres
Example 3 - 400 miles on 10 gallons
❓ Frequently Asked Questions
🔗 Related Calculators
How do you calculate MPG?
Divide the miles driven by the US gallons of fuel used. If you drove 300 miles on 12 gallons, MPG = 300 / 12 = 25 miles per gallon. For the most accurate figure, measure over a full tank rather than a short trip, since driving conditions vary.
How do I convert MPG to litres per 100 km?
Litres per 100 km and MPG are reciprocals with a unit factor. The quick conversion is 235.2 divided by US MPG. So 25 US MPG is about 235.2 / 25 = 9.4 litres per 100 km. This calculator shows both figures at once from your distance and fuel.
What is the difference between US and UK MPG?
The gallons differ. A US gallon is 3.785 litres and a UK (imperial) gallon is 4.546 litres. Because the UK gallon is about 20 percent larger, the same car shows a higher number in UK MPG than in US MPG. This calculator reports US MPG.
What is a good MPG for a car?
It depends on the vehicle type. A small modern petrol car often returns 35 to 50 US MPG, a mid-size car 25 to 35, and a large SUV or truck 15 to 22. Hybrids can exceed 50 US MPG. Compare your measured figure against the official rating to judge your driving efficiency.
How do I calculate fuel cost per mile?
Multiply the fuel used by the price per unit to get the total fuel cost, then divide by the miles driven. If 12 gallons at 3.50 per gallon cost 42, and you drove 300 miles, the cost per mile is 42 / 300 = 0.14. Enter a fuel price in the calculator to see this automatically.
Why is my real MPG lower than the sticker figure?
Official ratings come from standardised lab tests. Real driving involves cold starts, traffic, hills, air conditioning, cargo, and individual driving style, all of which lower economy. It is normal to see real-world MPG 10 to 25 percent below the official combined figure.
Does this MPG calculator work with kilometres and litres?
Yes. You can enter the distance in miles or kilometres and the fuel in US gallons or litres, and the calculator converts internally. It always reports US MPG, litres per 100 km, and km per litre so you can read whichever measure you prefer.
How can I improve my car's fuel economy?
Drive smoothly with gentle acceleration and braking, keep to steady speeds on the highway, maintain correct tire pressure, remove unnecessary weight and roof racks, and keep up with servicing. These habits can improve real-world MPG by 10 to 20 percent.