Fuel Cost & Fuel Economy Calculator
Trip cost = distance ÷ fuel efficiency × fuel price. A 300-mile trip at 30 mpg with fuel at $3.50 a gallon costs about $35.
Trip cost
$35
Fuel used
10 gal
Show the math
- 1
Divide distance by fuel efficiency
300 mi ÷ 30 mpg = 10 gal
= 10 gal
Read the steps as text
- Divide distance by fuel efficiency. 300 mi ÷ 30 mpg = 10 gal
- Multiply by the price per gallon. 10 gal × $3.5 = $35
Working out a trip's fuel cost
The calculator first finds how much fuel the trip needs by dividing distance by fuel efficiency — in US units, miles divided by miles-per-gallon gives gallons needed. Multiplying that by the price per gallon (or per litre in metric units) gives the total cost.
In metric units, fuel efficiency is usually given as litres per 100 km rather than distance per litre, so the calculator scales your trip distance to a 100 km basis first: (distance ÷ 100) × L/100km.
Working out your fuel economy
To find your actual fuel economy rather than assume a number, fill up, reset your trip odometer (or note the mileage), drive as normal, then fill up again and enter the distance covered and fuel added. Dividing distance by fuel used gives mpg (US) or, in metric, dividing fuel used by distance and scaling to 100 km gives L/100km.
Note that mpg and L/100km run in opposite directions: a higher mpg means better economy, while a lower L/100km means better economy — worth keeping in mind if you're used to one system and comparing to the other.
Frequently asked questions
- How do I calculate the fuel cost of a road trip?
- Divide the distance by your vehicle's fuel efficiency to get fuel needed, then multiply by the price per gallon or litre. This calculator does both steps for you.
- How do I find my car's actual fuel economy?
- Fill the tank, note the odometer reading, drive normally, then fill up again and record both the distance covered and the fuel needed to refill. Enter those into the 'Fuel economy' mode above.
- Why does a lower number mean better economy in L/100km but not in mpg?
- They measure opposite things: mpg is distance per unit of fuel (higher is better), while L/100km is fuel per unit of distance (lower is better). Both describe the same efficiency, just inverted.