Race Fuel Calculator

Race Fuel Formula

Fuel budget = (remaining race laps + extra racing laps + reserve-equivalent laps) × fuel per lap

Choose the Remaining Race Distance

Use Known laps when you have a reliable remaining lap count. For a timed race, enter the time remaining and the representative lap time. The calculator divides duration by lap time and rounds upward to a whole lap. This is an explicit planning assumption, not a prediction of the official lap count. Extra racing laps are then added separately. Set extra laps to zero when the known lap count already includes the finish procedure.

Separate Racing Laps from Reserve Fuel

Extra racing laps increase the planned distance. Reserve laps express additional fuel as a multiple of your consumption per lap and can be fractional. A reserve of 0.5 at 2.5 liters per lap adds 1.25 liters. It does not say that the race contains half an extra lap. The tool uses the same consumption rate for both racing and reserve amounts.

Worked Example: Fuel to Add

For 30 remaining laps, one extra racing lap, one reserve-equivalent lap, and 2.5 liters per lap, the budget is 32 × 2.5 = 80 liters. With 10 liters onboard, the additional requirement is 70 liters. A 100-liter tank has 90 liters of room, so all 70 liters can be added now. The budget includes the onboard fuel; adding the full 80 liters would count those 10 liters twice.

Tank Capacity and Later Refueling

Fuel to add now is the smaller of the additional requirement and available tank space. Any remaining requirement is reported as fuel to obtain later. That number is a volume, not a pit-stop count or a pit schedule. The full-tank racing-lap estimate is the whole number of laps available after subtracting the selected reserve-equivalent laps. It assumes the entered tank capacity is usable fuel. If the total budget exceeds capacity, a single tank cannot cover that budget at the stated consumption.

Units and Consumption Inputs

Each volume has its own unit selector. One US gallon equals 3.785411784 liters; one Imperial gallon equals 4.54609 liters. A gallon value must use the correct gallon definition. Enter measured fuel per lap for comparable conditions, rather than a distance-based consumption figure. Zero onboard fuel, zero extra laps, and zero reserve are accepted. Blank onboard, extra and reserve inputs mean zero; entered values apply even when their section is closed. Tank capacity is optional: omit it to calculate only the fuel budget and extra fuel requirement. Consumption, entered tank capacity and remaining race distance must be positive.

Timed-Race Assumptions

For 60 minutes remaining and 90 seconds per lap, the initial estimate is 40 laps before extra and reserve laps. A timed event can depend on the leader, when the timer expires, class position, caution periods, and the finish rules. iRacing AutoFuel uses leader pace and observed fuel consumption when estimating its own requirement. This calculator uses only the duration and lap time you enter. Recalculate as the forecast or consumption changes; it does not model traffic, fuel saving, formation laps, or refueling time.

Reference Table

Sources

iRacing Support, How to Use AutoFuel, updated 2026. Unit conversions and fuel-budget examples are calculated from the stated inputs.