⛽ Gas Cost Calculator: Estimate Trip Fuel Cost

What is the Gas Cost Calculator?

Working out the gas cost of a trip comes down to two questions: how much fuel will the journey use, and what does that fuel cost. In US units the fuel used is simply the distance divided by your miles per gallon, because MPG tells you how far one gallon takes you. Multiply that fuel by the price per gallon and you have the total cost. A 300 mile trip in a car that does 30 MPG uses 300 / 30 = 10 gallons, and at $3.50 a gallon that is 10 times 3.50 = $35.00. This is the same formula the U.S. Department of Energy publishes: fuel cost equals trip distance divided by vehicle MPG, multiplied by the fuel price.

Metric figures work a little differently because fuel economy is quoted as liters per 100 km (L/100km) rather than distance per unit of fuel. Here the fuel used is the distance divided by 100, multiplied by the L/100km figure. A 480 km trip at 8 L/100km uses 480 / 100 times 8 = 38.4 liters, and at 1.60 per liter that is about 61.44 in fuel. Note that a lower L/100km is more efficient, the opposite direction to MPG where higher is better, which often trips people up when comparing cars across regions. To convert between the two, divide 235.215 by the MPG figure to get L/100km, and vice versa.

The round trip option matters more than it looks. People routinely plan around the one way distance and then get surprised at the pump, because the journey home costs exactly as much as the journey out. Ticking round trip doubles the distance the calculator uses, so the total, the fuel and the cost per person all reflect the full there and back journey rather than half of it. For a daily commute, take the round trip figure and multiply by your working days to see the real weekly or monthly gas bill.

Splitting the cost is the other everyday use. If four people share a ride, the cost per person is the total divided by four, which makes a long drive far cheaper per head than driving alone and is the simplest way to agree a fair share of gas money. The cost per mile or per km figure is handy for a different reason: it lets you compare this trip with other journeys, set a mileage charge, or sanity check whether driving is cheaper than the train or a flight for the same route.

Fuel prices and vehicle economy are the two levers that move your result the most, and both swing widely. The U.S. Energy Information Administration tracks pump prices that can shift by a dollar a gallon within a single year, and the average new US car returns roughly 25 MPG while efficient hybrids top 50 MPG. Because cost scales directly with price and inversely with MPG, a thirsty SUV on expensive gas can cost two to three times more than an economical hybrid on the same route, which is why plugging in your own real numbers beats relying on a rough guess.

One caveat: this tool estimates the fuel bill, not the full cost of driving. Diesel, for example, usually costs more per gallon than regular gasoline but delivers 20 to 30 percent better economy, so its cost per mile can still come out lower. Electric vehicles are priced per kWh rather than per gallon entirely. Tolls, parking, insurance, tyres and depreciation all sit on top of the gas figure, so treat the number here as the fuel floor for a trip rather than its total price.

When to use it

• Budgeting the fuel cost of a road trip or daily commute before you leave so there are no surprises at the pump.
• Splitting gas money fairly between everyone in a carpool or rideshare down to the cent.
• Comparing the running cost of two vehicles by their cost per mile on the same trip, such as a hybrid versus an SUV.
• Deciding whether to drive or take the train, bus or a flight by checking the per mile cost against a ticket price.
• Estimating a monthly or annual fuel budget by multiplying one trip cost by how often you drive it.
• Setting a fair mileage reimbursement rate for work travel based on real fuel cost per mile.

How to use the Gas Cost Calculator

1. Pick your unit system: US (miles, MPG, price per gallon) or metric (km, L/100km, price per liter).
2. Enter the trip distance, your vehicle fuel economy and the current fuel price from a receipt or a live price app.
3. Tick round trip if you are driving there and back, and set how many people are sharing the cost.
4. Read off the total fuel cost, gallons or liters used, cost per person and cost per mile.
5. Copy the result or adjust any input to compare scenarios, such as a cheaper gas price or a more efficient car.

Formula & method

Worked examples

Approximate fuel cost for a 300 mile trip by MPG and gas price (US units)

Typical fuel economy and cost per mile by vehicle type (at $4.30 per gallon)

Quick conversions between US and metric driving figures

Common mistakes to avoid

• Forgetting the return journey. Entering only the one way distance for a round trip halves your estimate. If you are driving there and back, tick the round trip box so the distance, total and cost per person all cover the full journey.
• Mixing up MPG and L/100km. With MPG a higher number is more efficient, but with L/100km a lower number is more efficient. Typing an L/100km value into an MPG field, or the reverse, gives a wildly wrong cost, so set the right unit mode first.
• Using the brochure MPG instead of your real economy. Official MPG is measured in ideal conditions. Real economy in city traffic, cold weather or with a loaded car is usually lower, so the true gas cost is often higher than the sticker number suggests. Track a few tank fills to find your real figure.
• Treating gas as the only cost of a trip. This tool estimates fuel only. Tolls, parking, wear on tyres and brakes, insurance and depreciation all add to the real cost of driving, so the gas figure is a floor, not the full price of the journey.
• Comparing diesel and gasoline on price per gallon alone. Diesel usually costs more per gallon but returns 20 to 30 percent better economy, so its cost per mile can be lower. Always compare on cost per mile, not the pump price, when weighing up fuel types.
• Using an old gas price. Pump prices can move by a dollar a gallon within a year. A stale price quietly throws off a whole monthly budget, so pull the current local price before you rely on the number for planning.

Glossary

Gas cost

The total price of the fuel a trip uses, found by multiplying the fuel used by the price per unit.

Fuel efficiency

How far a vehicle travels on a unit of fuel, shown as MPG in US units or L/100km in metric units.

MPG

Miles per gallon, the US and UK fuel economy measure where a higher number means a more efficient car.

L/100km

Liters of fuel used per 100 kilometres, the metric economy measure where a lower number is more efficient.

Round trip

A there and back journey, which uses double the one way distance and therefore double the fuel.

Cost per mile

The total trip cost divided by the distance, useful for comparing journeys or setting a mileage charge.

Gallons needed

The amount of fuel a trip consumes, equal to the distance divided by the vehicle MPG in US units.

kWh

Kilowatt hour, the unit electricity is priced in and the basis for an electric vehicle running cost instead of gallons.

Frequently asked questions

Sources

• Gas Mileage Tips and Fuel Economy , U.S. Department of Energy, fueleconomy.gov
• Gasoline and Diesel Fuel Update , U.S. Energy Information Administration
• 2026 Fuel Economy Guide , U.S. Department of Energy and EPA