Clear formulas for l/100 km, trip fuel use and cost, plus how to measure real consumption after refuelling. Enter your own €/L price.
This guide explains how to calculate fuel consumption (l/100 km), trip fuel use and cost, and when it is practical to use the 777.ee fuel cost calculator. You enter the price (€/l) yourself — the guide does not rely on a changing market price.
Formulas (same model as the calculator)
The 777.ee calculator uses a simple deterministic model:
• fuel_l = km × (l_per_100km / 100)
• cost_€ = fuel_l × price_€_l
• per passenger = cost_€ / passenger_count
Consumption is litres per hundred kilometres, not per kilometre — hence the division by one hundred. Distance and consumption rate together determine litres used; the per-litre price determines the cost.
Example (calculator defaults): 100 km, 6.5 l/100 km, €1.60/l
• fuel = 100 × 0.065 = 6.5 l
• cost = 6.5 × 1.60 = €10.40
• split between two passengers = €5.20 each
Cost per 100 km
To see what 100 km costs in fuel, the same model applies:
• cost_per_100km = l_per_100km × price_€_l
For example, 6.5 l/100 km × €1.60/l = €10.40 / 100 km. That matches the 100 km trip cost in the example above.
How to measure actual consumption after refuelling
Manufacturer test-cycle figures and your vehicle’s real-world consumption can differ. Measuring your own is more reliable:
1. Fill the tank and note the odometer/trip.
2. Drive at least a couple of hundred kilometres in normal conditions.
3. Fill to the same level again.
4. Calculate: l_per_100km = (litres_added / km_driven) × 100
A trip-computer average is a fair approximation if it has accumulated for a long stretch since the last reset.
Common mistakes
• Entering consumption as l/km instead of l/100 km (missing ×100 or /100).
• Counting only one direction instead of a return trip.
• Using a summer data-sheet figure for short winter trips.
• Expecting live pump prices from the calculator — price is entered manually.
• Treating a passenger split as the full cost of running the car (depreciation, insurance and tyres stay outside).
What the result means
The result estimates fuel use and cost for a trip or period in a combustion-engine vehicle. The model does not separately model speed, load, air conditioning or winter mode — those show up only when you enter a realistic consumption figure. It is not for electric vehicles (kWh/100 km).
When to use the 777.ee calculator
Manual arithmetic is fine for a one-off check. If you want to try different distances, consumption figures, prices or passenger counts quickly, use the localised fuel cost calculator — it applies the same formula without retyping the steps.Fuel cost calculator