Automotive Tools
Calculate your vehicle's fuel economy in MPG or km/L, and track cost per distance.
Fuel Economy
25.00 MPG
9.41 L/100km
Enter miles driven and gallons consumed. MPG = miles / gallons. Lower L/100km is better fuel economy.
A gas mileage calculator is a fuel-efficiency tool that divides distance travelled by fuel consumed to yield economy metrics. It works in both US (miles and gallons, output in MPG) and metric (kilometres and litres, output in km/L or L/100km) units. The calculator also converts between all three formats and optionally calculates cost per distance when you input fuel price.
The calculator takes distance driven and fuel used, then applies one of two formulas depending on your unit system. US mode divides miles by gallons to get MPG; metric mode divides km by litres to get km/L. Both are then cross-converted: MPG translates to km/L by scaling distance and fuel by their conversion factors, and L/100km (a common European metric) is derived by inverting the relationship. If you supply fuel price, cost per distance is calculated by multiplying fuel consumed by price per unit, then dividing by distance.
MPG = distance (mi) ÷ fuel (gal); km/L = distance (km) ÷ fuel (L); L/100km = (fuel (L) × 100) ÷ distance (km); Cost per mi = (fuel (gal) × price per gal) ÷ distance (mi)MPG and km/L directly measure distance per unit of fuel. L/100km inverts this perspective, showing how much fuel is needed to travel 100 km (lower is better). Cost-per-distance metrics multiply fuel volume by unit price and divide by total distance, yielding running cost per mile or kilometre.
| Input | Result | Notes |
|---|---|---|
| Distance: 300 miles, Fuel: 12 gallons, Fuel Price: $3.50/gal | 25 MPG | 10.62 km/L | 9.41 L/100km | Cost: $0.14/mi | Total: $42.00 | A typical sedan's fuel economy. At $3.50/gal, this driver spends 14 cents per mile. |
| Distance: 480 km, Fuel: 45 litres, Fuel Price: $1.20/L | 10.67 km/L | 16.87 MPG | 9.38 L/100km | Cost: $0.11/km | Total: $54.00 | Same efficiency as above but in metric. The metric calculation confirms the cross-conversion is consistent. |
| Distance: 500 miles, Fuel: 20 gallons, Fuel Price: $3.80/gal | 25 MPG | 10.62 km/L | 9.41 L/100km | Cost: $0.152/mi | Total: $76.00 | Slightly worse fuel price but same MPG; total cost scales with fuel price. |
EPA estimates are measured in controlled lab conditions (level road, steady speed, new engine). Real-world driving includes idling, acceleration, cargo, and weather, all of which reduce efficiency. Expect 15–25% worse fuel economy in daily driving than EPA ratings.
Both are valid; L/100km is common in Europe and Australia and has an intuitive advantage: lower numbers always mean better economy. MPG is standard in the US. The calculator converts both, so use whichever you prefer.
It depends on vehicle type: compact cars often achieve 28–35 MPG, sedans 20–30 MPG, SUVs 15–25 MPG, and trucks 15–20 MPG. Compare your result to your manufacturer's estimate; if consistently worse, check tyre pressure, alignment, and engine maintenance.
For purest fuel-economy measurement, use distance from odometer at fill-up; the odometer doesn't measure idling or parking. Idling time is already factored into real-world MPG if you're measuring fill-to-fill consumption on actual roads.
Sum all miles driven across trips, sum all gallons consumed, then divide miles by gallons. Do not average individual MPG values; the weighted average accounts for trips of different lengths or fuel amounts.
Yes. Cold engines run inefficiently, and cold oil is thicker, increasing friction. Expect 10–15% worse fuel economy in winter. Warming up your car before driving and keeping it in a garage helps slightly.