This estimates fuel cost for a trip, from the distance and the vehicle’s fuel economy — useful for budgeting a road trip or comparing what two different vehicles would cost for the same journey.
How it works
Fuel cost
cost = (distance ÷ fuel economy) × price per unit of fuel
In mpg mode, distance divides by miles-per-gallon to get gallons used. In L/100km mode, the relationship inverts the other way — litres used is (distance ÷ 100) × L/100km, since that figure is already volume per distance rather than distance per volume.
Why better fuel economy divides the cost, not multiplies it
A more efficient car — a bigger mpg number — uses less fuel for the same distance, which is why fuel economy sits in the denominator: double the mpg, and the identical trip costs exactly half as much in fuel. This is the same distance-per-volume relationship the fuel economy converter’s own documentation explains, applied here to a cost estimate instead of to a unit conversion.
How to use this calculator
- Pick mpg (US) or L/100km, whichever matches how your vehicle’s economy is quoted.
- Enter the trip distance, fuel economy, and current fuel price.
- Read the estimated cost and fuel used.
Frequently asked questions
Why is this only an estimate?
Real fuel economy varies with driving style, terrain, load, traffic and weather — the mpg or L/100km figure entered is a stated average, and actual consumption on any specific trip will differ somewhat from it.
Does this work for UK imperial mpg?
The mpg mode here uses the US gallon specifically. UK (imperial) mpg is a different, larger unit — convert it to US mpg or to L/100km first using the fuel economy converter, since mixing the two mpg figures directly would understate the true cost.
How does this help compare two different vehicles?
Run the same trip distance and fuel price through both vehicles’ fuel economy figures — the cost difference is a direct, apples-to-apples comparison of what that specific trip would actually cost in each.
Should I include the cost of tolls or parking?
No — this calculates fuel cost only. Tolls, parking and other trip expenses need to be added separately for a full trip budget.
Why does doubling the distance exactly double the cost?
Because fuel cost scales linearly with distance at a fixed fuel economy and price — twice the distance means twice the fuel used, and twice the fuel used means twice the cost, all else held constant.
