What will the trip cost in fuel?
Three numbers decide it: how far you are driving, how thirsty your vehicle is, and what fuel costs where you will buy it. Enter them and this calculator returns the fuel the trip will burn and its cost, plus the cost per mile (or per 100 km) and the round-trip figure — the two numbers that make budgeting and comparing routes or vehicles easy. It works in US units (miles, miles per gallon, dollars per gallon) and metric units (kilometres, litres per 100 km, price per litre).
The formula, and the mpg trap
The two efficiency systems run in opposite directions: with mpg, higher is better; with L/100 km (a consumption figure), lower is better. They convert through the constant 235.215 — divide it by either figure to get the other — and the stats panel shows the equivalent so you can compare a European spec sheet with an American one. For honest results use real-world efficiency: motorway cruising beats the official figure's lab conditions, while cold weather, roof boxes, low tyre pressure and city traffic all make it worse, typically by 10–20%.
Using the answer
Cost per mile is the figure transport businesses live by: multiply it by any distance to price a journey, compare two vehicles over the same trip, or work out a fair contribution when car-sharing (split the result with the Split Bill Calculator). If the round-trip number shocks you, the levers ranked by effect are usually: drive less (route), drive slower (aerodynamic drag rises steeply past 65 mph), then vehicle efficiency itself.
Worked example
A 300-mile trip in a car doing 30 mpg with fuel at $3.50 a gallon burns exactly 10 gallons and costs $35.00 — $70 for the round trip.
How to use this calculator
- Choose US or metric units.
- Enter the trip distance and your vehicle's real efficiency.
- Enter the fuel price you expect to pay.
- Read the trip cost in the green panel, with fuel used and per-mile cost in the table.
Electric vehicles, same idea
For an EV, swap gallons for kilowatt-hours: distance × consumption (kWh per 100 miles or km) × price per kWh. A car using 30 kWh per 100 miles driven 300 miles uses 90 kWh; at $0.16 per kWh that is $14.40 — the same arithmetic this page does, with different labels.