How do I calculate fuel cost for a trip?

Divide distance by fuel economy for the fuel used, then multiply by the price.

Does driving faster use more fuel?

Yes; economy drops noticeably above about 60 mph due to air resistance.

Fuel Cost for a Road Trip

Published 9/22/2025 · 3 min read · Car calculators

Marco Bianchi — Home, DIY & motoring writer at OneKitly

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In short

To work out a trip's fuel cost, divide the distance by your car's fuel economy to get the fuel used, then multiply by the price per unit. For a 400-mile trip at 30 mpg and $3.20 a gallon: 400 ÷ 30 = 13.3 gallons, × $3.20 = $42.70. In metric, divide the km by 100, multiply by L/100 km for litres, then times the price per litre.

A car on a rural road with mountains in the distance. — Matheus Bertelli · Pexels · Pexels

Divide distance by fuel economy, then multiply by the price. Here's the calculation, metric vs mpg, what pushes it up, and how to split the cost.

The calculation

A trip's fuel cost is the fuel you'll burn times its price. First find the fuel: divide the distance by how far your car goes per unit of fuel. A car doing 30 mpg over a 400-mile trip burns 400 ÷ 30 = 13.3 gallons. Then multiply by the pump price: at $3.20 a gallon, that's $42.70. Two simple steps — fuel used, then fuel cost — and you have the number before you leave the driveway.

Metric vs mpg

The two systems read opposite ways, so don't mix them up. Litres per 100 km measures fuel for a fixed distance, so lower is better — 5 L/100 km beats 8. Miles per gallon measures distance for a fixed fuel, so higher is better — 50 mpg beats 30. For an mpg car, divide the miles by the mpg to get gallons, then multiply by the price per gallon. Whichever you use, just keep distance, economy and price in matching units.

What pushes it up

Real-world fuel use rarely matches the brochure figure, and several things widen the gap. Speed is the big one: above about 60 mph, air resistance climbs steeply, so cruising faster burns noticeably more. A heavy load, a roof box, under-inflated tyres, running the air conditioning and lots of hills all add up. Stop-start city traffic is thirstier than a steady motorway cruise. Use your own recent economy, not the official number, for a realistic estimate.

Compare and split

Once you have the total, two moves make it more useful. Reduce it to a cost per mile (or per 100 km) so you can compare cars, routes or a different fuel price at a glance. And if you're carpooling, divide the total by the number of people — a $43 tank across four passengers is about $11 each, which is where a road trip often beats the train or a flight. The same figures also let you weigh driving against other ways to make the journey.

Worked with our own calculator

Fuel cost calculator

Given

Distance (km): 500
Consumption (L/100 km): 6.5
Fuel price (per L): $1.80

Result

Fuel needed (L): 32.5
Total cost: $58.50

These figures are produced by the calculator below, not typed in by hand — they are recomputed whenever the tool changes.

Run it on your own figures →

Frequently asked questions

How do I calculate fuel cost for a trip?: Divide distance by fuel economy for the fuel used, then multiply by the price.
How much fuel for a 400-mile trip?: At 30 mpg, about 13.3 gallons.
Does driving faster use more fuel?: Yes; economy drops noticeably above about 60 mph due to air resistance.

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