Fuel Cost Calculator
Trip fuel cost from distance, consumption (L/100 km) and fuel price — liters needed, total and per-km cost.
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How It Works
Total fuel cost follows one chain of arithmetic: liters needed = distance ÷ 100 × consumption (when consumption is quoted as L/100 km), then cost = liters × price per liter. Drive 450 km in a car rated at 6.5 L/100 km, with fuel at $1.10/L, and the math runs 450 ÷ 100 × 6.5 = 29.3 liters, then 29.3 × $1.10 ≈ $32.23 — about $0.072 per km, the figure the calculator surfaces so you can compare against transit fares or split cost fairly among passengers.
The part that trips people up is that fuel-efficiency units point in opposite directions. In L/100 km, a lower number is better — less fuel burned to cover the same distance. In miles per gallon (mpg), a higher number is better — more distance out of the same gallon. Comparing "6 L/100 km" against "40 mpg" by eyeballing the digits gives a nonsense answer, because one scale measures fuel-per-distance and the other measures distance-per-fuel. The correct conversion is L/100 km = 235.21 ÷ mpg (US gallon), so 40 mpg ≈ 5.9 L/100 km — actually close in efficiency to a car quoted at 6 L/100 km, not obviously better or worse as the raw digits might suggest.
What to Know
Catalog consumption figures come from standardized lab cycles and rarely match real-world driving. City stop-and-go, air conditioning, a cold engine, a roof box, or a fully loaded car all push real consumption 10-20% above the sticker value — sometimes more. Steady highway cruising at moderate speed is the one condition where catalog numbers come close to reality.
Speed matters more than most drivers expect, because aerodynamic drag scales with the square of speed: going from 100 km/h to 130 km/h does not add 30% more drag, it can add 60-70%, which is why fuel use per km often jumps 15-25% at that higher cruising speed. The calculator's per-km cost figure makes it easy to test scenarios — a longer highway route can sometimes cost less than a shorter one dominated by urban stop-and-go.
- Measure your own real consumption by resetting the trip computer at a full tank, then dividing liters refilled by kilometers driven at the next fill-up.
- Average two or three tanks to smooth out weather, traffic, and route differences.
- Use the per-km figure to fairly split costs on shared trips or to compare a road trip against a flight or train ticket.
Frequently Asked Questions
How do I find my real consumption?
Fill the tank, reset the trip odometer, drive normally, refill: liters refilled ÷ km driven × 100. Two or three tanks average out weather and traffic so the figure reflects your actual driving, not the lab test.
Does speed change the math?
Strongly — aerodynamic drag grows with speed squared, not linearly. Most cars burn 15-25% more fuel per km at 130 km/h than at 100 km/h; stop-and-go city traffic is also far above the steady highway figure.
How do I split cost among passengers?
Divide the total by the number of people — the per-km output also makes it easy to charge a partial leg fairly if someone only rides part of the route.
How do I convert between L/100 km and mpg?
They are inverse scales, so a straight number comparison is wrong. Use L/100 km = 235.21 ÷ mpg (US gallon), or mpg = 235.21 ÷ (L/100 km). A car at 30 mpg is roughly 7.8 L/100 km — plug either figure into the calculator once converted.
Does driving style matter more than the car itself?
Often yes — harsh acceleration, high cruising speed, and unnecessary idling can shift consumption by 20-30% regardless of the vehicle. Two identical cars driven differently can post very different real-world numbers even though the catalog rating is the same.
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