Calculate the total fuel cost for any trip from distance, fuel efficiency, and price per litre or gallon — with round-trip and side-by-side two-vehicle comparison support.
It's tempting to estimate fuel cost with a rough mental shortcut, but doing it properly requires factoring in your vehicle's actual efficiency, since two vehicles covering the identical distance can have wildly different fuel costs. A vehicle rated at 10 L/100km burns 43% more fuel over the same distance than one rated at 7 L/100km, and that gap compounds directly into cost — which is exactly why efficiency, not just distance and price, is the input that actually determines your total spend. This tool takes all three inputs together — distance, efficiency, and price — because leaving any one of them out of a mental estimate is the most common source of budgeting surprises on longer trips.
These two units measure the same underlying thing — fuel consumed per distance traveled — but express it in inverted ways, which is genuinely worth understanding rather than just treating as a unit-conversion inconvenience. L/100km directly answers 'how much fuel does this distance cost me,' scaling linearly with both distance and fuel usage — this makes it intuitively easier to reason about total trip cost. MPG answers a different question — 'how far can I go per unit of fuel' — which is intuitive for comparing efficiency between vehicles, but genuinely misleading when reasoning about savings, because the same MPG improvement saves very different amounts of fuel depending on the starting efficiency (a jump from 10 to 20 MPG saves far more fuel over a fixed distance than a jump from 40 to 50 MPG, despite both being +10 MPG). This is a well-documented cognitive bias studied by transportation researchers, and it's a big part of why L/100km is generally considered the more intuitive unit for actual cost planning.
A one-way distance figure understates real-world fuel spending for the vast majority of everyday trips — nearly every commute, errand run, or visit involves returning to your starting point, doubling the actual fuel consumed even though the 'trip' in casual conversation often only refers to the outbound leg. The Round Trip toggle handles this directly rather than requiring you to remember to double your distance input manually. For a genuinely useful budget picture, it's also worth multiplying a single round-trip cost by how often you make that trip — a $12 daily commute cost becomes roughly $260 a month or over $3,000 a year on a 5-day work week, a figure that's far more meaningful for actual financial planning than the per-trip number alone.
Comparing two vehicles' fuel costs over an identical trip is most useful when the comparison maps to a real decision you're actually facing: choosing between two cars before a purchase, deciding whether a more expensive but more efficient hybrid pays for itself over your typical driving, or simply understanding how much a daily commute would cost in a different vehicle you're considering. The comparison becomes especially valuable when scaled up — a $3 per-trip difference feels trivial in isolation, but the same gap repeated over a daily commute, a year of ownership, or the full life of a vehicle can represent a genuinely significant total cost difference worth factoring into a purchase decision.
Fuel Cost Calculator estimates real trip and commute costs. These related calculators cover other everyday travel and unit math.