Fuel Cost Calculator — trip cost, per-person split, L/100km ⇄ MPG

Real-world use cases

• Price a weekend road trip before you commit

  You are weighing a 480 km drive to the coast against the train. Punch in 480 km, your car's 6.8 L/100km, and the local pump price of €1.85/litre, tick "round trip", and you have the real fuel number — about €120 there and back — in two seconds. Now it is a fair comparison against the rail fare, instead of a vague "fuel is probably cheaper" hunch that road-trippers always lose money on.

• Settle a carpool fairly

  Four of you split a 300-mile drive to a wedding. Enter the distance, the driver's 32 US MPG, the $3.60/US-gallon price, set people to 4, and the per-person figure is the exact amount each passenger Venmos the driver. No "just give me twenty bucks" awkwardness — a defensible number everyone can see.

• Convert a foreign car review's economy figure

  A British review raves that a hatchback does "55 MPG". You think in L/100km. Open the converter tab, type 55, pick MPG (UK), and read 5.14 L/100km — genuinely frugal. Had you assumed US gallons you would have read 4.28 L/100km and overestimated the efficiency by ~20%.

• Build a defensible mileage-reimbursement number

  Your employer reimburses fuel, not a flat per-mile rate. Log your trip distance, your car's actual economy, and the receipt price, and the per-km / per-mile cost gives you a line item you can attach to the expense report — derived from real numbers, not a guess.

• Compare two cars you are deciding between

  One car is rated 7.5 L/100km, the other 6.0. Run your typical annual distance through both at today's fuel price and the cost gap stops being abstract — it becomes "this one costs me €310 more a year in fuel", which is the number that actually moves a buying decision.

Common pitfalls

• Comparing a US MPG figure against a UK MPG figure as if they were the same. They are not — a UK gallon is 20% bigger, so for the same MPG number "40 MPG (US)" is actually the more efficient car (it went 40 miles on less fuel). Always confirm which gallon the source used before comparing two cars.

• Treating L/100km and MPG as if they scale linearly. They are reciprocals — improving from 8 to 6 L/100km saves far more fuel than improving from 6 to 4 the same "2 units" suggests. Compare in L/100km (or cost) when you care about money, not in raw MPG steps.

• Forgetting that the price unit must match the pump. If you set "price per US gallon" but typed the per-litre price, the cost comes out ~3.8× too low. Check the unit dropdown next to the price matches what is actually on the receipt.

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