How to estimate the fuel cost of a road trip
A practical guide to turning distance, fuel economy and pump price into a reliable fuel budget, plus the factors that move real costs.
The three numbers you need
A fuel estimate rests on just three inputs: how far you are driving, how efficiently your vehicle uses fuel, and what fuel costs right now. Distance comes from a maps app or your route. Fuel economy is on the window sticker or, more honestly, your own trip computer average. Price is whatever the pump reads on the day. With those in hand the math is short, and this calculator does it the moment you type.
Doing the arithmetic
In US units you divide the distance by miles per gallon to get gallons, then multiply gallons by the price per gallon. A 300 mile drive at 30 MPG needs 10 gallons, and at $3.50 a gallon that is $35.00. Metric flips the efficiency figure around: multiply the distance in hundreds of kilometres by the litres per 100 km, then multiply by the price per litre. A 600 km trip at 8 litres per 100 km burns 48 litres.
Why real costs drift higher
Published fuel economy comes from gentle test cycles that rarely match a loaded car on a summer highway. Speeds above about 55 miles per hour raise drag sharply, roof boxes and bike racks add more, and stop start city traffic wastes fuel at every light. Cold starts, running the air conditioner and under inflated tyres each chip away at your MPG. Padding the estimate by ten to fifteen percent is a sensible cushion for a long journey.
Budgeting a round trip
For a there and back journey, tick the round trip box so the distance doubles before the fuel is worked out. A 150 mile each way commute becomes 300 miles, which at 25 MPG is 12 gallons and $48.00 at $4.00 a gallon. If several people share the ride, dividing that total is a fair way to split costs. Remember the figure is fuel alone, so add tolls and parking for the true out of pocket amount.