Fuel Cost Calculator

Before a long drive, the practical question is simple: how much will the fuel actually cost? This calculator answers it from three numbers you already know or can look up — the distance you'll drive, how far your vehicle travels per unit of fuel, and the price at the pump. It then works out the total fuel bill, the volume of fuel you'll burn, and — if you're carpooling — an even split per passenger.

It speaks every common way of quoting fuel economy: US MPG, Imperial (UK) MPG, km/L and L/100km. Pick the convention that matches your car's sticker or trip computer and the calculator handles the arithmetic and the units for you.

There are two families of fuel-economy units, and they use mirror-image formulas. Most ratings measure distance per unit of fuel (higher is better), where the fuel used is distance divided by economy:

fuel used = distance ÷ fuel economy
total cost = fuel used × fuel price
cost per person = total cost ÷ passengers

The metric L/100km rating is the inverse — it measures fuel per unit of distance (lower is better), so the volume is multiplied rather than divided:

fuel used (L) = distance (km) × consumption ÷ 100
total cost = fuel used × price per litre

Take a 300-mile trip in a car that does 25 US MPG, with fuel at $4.00 a gallon, shared by three people. Every figure below is produced by the same engine that runs the calculator above:

So the trip burns 12 gallons, costs $48.00 in fuel, and works out to $16.00 each. Change any input and the result scales linearly — double the distance and the cost doubles; halve the price and it halves.

For a fixed trip and price, the cost is driven almost entirely by how efficient your vehicle is. Here is the same 400-mile trip at $3.50 a gallon across a range of economies:

A car doing 50 MPG costs less than half what a 20-MPG SUV costs on the identical route. If you drive long distances regularly, that gap compounds — our LED Savings Calculator applies the same "small per-unit difference, big annual total" logic to household energy.

Distance and vehicle efficiency dominate the total, but how you drive moves the needle too — and it costs nothing to change. The U.S. Department of Energy's fueleconomy.gov reports that aggressive driving (rapid acceleration, hard braking, speeding) can cut fuel economy by roughly 15-30% at highway speeds and 10-40% in stop-and-go traffic, and that each 5 mph you drive above 50 mph is roughly equivalent to paying an extra $0.29 per gallon.

• An idling engine burns about a quarter to half a gallon of fuel per hour, depending on engine size and A/C use.
• Every extra 100 lbs of cargo trims fuel economy by roughly 1% — clear out unneeded weight before a long trip.
• Splitting the trip with more people directly cuts everyone's share — set the passengers field above to see how much a full carpool saves per person.

None of this changes the calculator's arithmetic — it changes what fuel-economy number is realistic to enter. If recent fill-ups show worse mileage than your car's rated MPG, use your own observed figure rather than the sticker rating so the cost estimate matches what you'll actually pay.

When you choose the L/100km convention, the tool converts internally using the exact constants below, so you can enter a European or Canadian consumption rating directly without doing the maths yourself:

• 1 US gallon = 3.785411784 litres; 1 Imperial gallon = 4.54609 litres; 1 mile = 1.609344 km.
• US MPG = 235.215 ÷ (L/100km) — e.g. 8 L/100km ≈ 29.4 US MPG.
• Imperial MPG = 282.48 ÷ (L/100km) — e.g. 8 L/100km ≈ 35.3 Imperial MPG.

Want to compare two vehicles on cost-per-distance rather than a single trip? The Fuel Cost per km Comparator is built for that, and the E20 Mileage Impact Calculator estimates how switching to an ethanol blend shifts your running cost. To turn any of these figures into a percentage change, our Percentage Calculator does the last step.

This is deterministic arithmetic, and it is only as good as the inputs you give it. Specifically:

• Fuel economy is treated as a single constant average over the whole trip — there is no adjustment for city versus highway driving, terrain, load, weather or driving style.
• Fuel price is a single figure for the entire trip; it does not model prices changing along the route.
• EPA and government-rated MPG / L-per-100km figures are test-cycle numbers that many drivers do not achieve day to day — real-world city driving can use 20-30% more fuel than the sticker suggests.
• Only priced fuel volume is modelled: no tolls, parking, wear-and-tear or non-fuel costs are included.
• Electric vehicles are out of scope — they consume electricity (kWh), not a priced fuel volume. Hybrids work if you enter their gasoline-mode economy.