Fuel Cost Calculator
How much will gas cost on your next road trip? Before you hit the interstate, it pays to know: fuel is usually the single biggest expense of any American road trip.
- Compare scenarios before you decide
- Clear, itemized figures
- Works on mobile, no sign-up
Fuel Cost Calculator
Enter your numbers and press Calculate
How to use the fuel cost calculator
If you think in miles, mpg and dollars per gallon, switch the "Unit system" selector to US gallons — no manual conversion needed. Enter four numbers and press Calculate:
1. Trip distance in kilometers or miles, depending on the unit system you picked (one way; double it for a round trip). 2. Average consumption in liters per 100 km, or your car's mpg in gallon mode. A 30-mpg sedan burns about 7.8 L/100km. 3. Price at the pump, per liter or per gallon to match your selection. 4. People splitting the cost, so everyone pays the same share.
The formula the calculator runs, in plain text:
liters = distance x consumption / 100 total cost = liters x price per liter cost per person = total cost / people
Worked example with the defaults: 400 km x 6.5 L/100km / 100 = 26 liters; 26 x $1.60 = $41.60 total, which for a solo driver is also $41.60 per person.
Real example: Los Angeles to Las Vegas
Two friends drive from Los Angeles to Las Vegas on I-15: about 270 miles, which is roughly 435 km. Their midsize sedan averages 28 mpg on the highway — converting, 235.215 / 28 = 8.4 L/100km. Gas along the route costs $3.60 per gallon, which is 3.60 / 3.785 = about $0.95 per liter.
Step by step: 435 x 8.4 / 100 = 36.54 liters (about 9.7 gallons). Multiply by the price: 36.54 x 0.95 = $34.71 for the one-way drive. Split two ways, that is 34.71 / 2 = $17.36 each — cheaper than most rideshare trips across town.
For the drive home, just double everything: about $69.43 total and $34.71 per person for the whole weekend. Note that this is fuel only; parking on the Strip is a separate line item. In a 22-mpg SUV (10.7 L/100km) the same one-way leg would run about $44.21, almost ten dollars more.
How to cut fuel costs (and the mpg question)
The consumption figure you enter is not fixed — it depends on how you drive. These habits make a real difference on a long American road trip:
- Tire pressure: check it cold before you leave. Running a few psi low can add roughly 2-4 % to consumption and wears the tires faster.
- Steady, moderate speed: pushing from 65 to 80 mph sharply increases aerodynamic drag and can burn 15-20 % more fuel. Cruise control pays for itself on the interstate.
- Look ahead: coasting toward a red light instead of braking late saves both gas and brake pads.
- Weight and aerodynamics: empty the trunk and remove the roof box or bike rack when unused — at highway speed a roof box can add 10-20 % to consumption.
- Shop around: gas price apps routinely show differences of 30-50 cents per gallon within the same city.
mpg vs. L/100km, demystified. American cars measure efficiency in miles per gallon, while this calculator uses liters per 100 km. The two scales are inverses of each other and the bridge is one constant: 235.215. To convert either way, divide 235.215 by the number you have. So 30 mpg = 235.215 / 30 = 7.84 L/100km, and 6.5 L/100km = 235.215 / 6.5 = 36.2 mpg. For the pump price, divide dollars per gallon by 3.785 to get dollars per liter.
Treat the result as an estimate: traffic, terrain, A/C and cargo can swing real-world consumption by 10-15 % either way.
Frequently asked questions
How do I find my car's real fuel consumption?
The most reliable method is the full-tank test: fill up until the pump clicks off, reset the trip odometer, drive 200-300 miles of mixed roads and fill up again at the same pump. Divide the liters (gallons x 3.785) by the kilometers and multiply by 100. The dashboard computer is a decent reference but typically reads 5-10 % better than reality.
Does this work for diesel, LPG or electric cars?
For diesel and LPG, yes: the formula is identical — just enter that fuel's consumption and price per liter. For electric vehicles it does not apply directly, since EVs consume kWh per 100 km instead of liters; the logic would be the same (kWh x price per kWh), but this tool's units are designed for liquid fuels.
My car shows mpg or km/L — how do I convert to L/100km?
If your car shows miles per gallon, divide the constant 235.215 by the mpg figure: 35 mpg equals 235.215 / 35 = 6.7 L/100km. The same operation works in reverse (235.215 / 6.7 = 35 mpg). If it shows kilometers per liter, divide 100 by that figure instead: 14 km/L equals 100 / 14 = 7.1 L/100km.
Why might my actual fuel spend differ from the estimate?
Because real-world consumption shifts with conditions: heavy traffic, mountain grades, air conditioning, rain, cargo weight or aggressive driving can move it 10-15 % either way. Pump prices also vary between stations and from day to day. Treat the result as a planning estimate and add a 10 % buffer for mountainous routes or predictable congestion. Tolls and parking are not included.
About this calculator
This calculator tells you in seconds how many liters (or gallons) you will burn, what that means in dollars, and how much each person owes when you split the bill. All you need are three numbers you already have: the distance, your car's average consumption, and the price at the pump. If your car reports mpg, the guide below shows the 10-second conversion.