How Long to Preheat a Pizza Stone

The short answer

Around 25 minutes after your oven says it has reached temperature, for a typical 15 mm cordierite stone. Around 40 minutes for a three-quarter-inch one. The oven's beep is about the air, not about the stone.

Put the stone in a cold oven, set the maximum, and start counting from the beep rather than from when you turned it on.

Times by surface

Where those numbers come from

Not from a stopwatch. From mass, specific heat capacity and a surface heat transfer coefficient, run through a lumped-capacitance model - which is legitimate here because the Biot number for every surface above sits at or below 0.1.

The time constant is mass times specific heat capacity, divided by the effective surface heat transfer coefficient times the exposed area. Three time constants gets you 95 percent of the way to oven temperature; 4.6 gets you 99 percent. Full derivation, constants and sources on the methodology page.

The one assumption is the heat transfer coefficient, taken as 20 W/m2.K. At 30 W/m2.K every figure above shortens by about a third. That range is why we say "about" and why the real recommendation is to measure.

Why the oven beeps too early

The thermostat is measuring air, and air has almost no thermal mass - it reaches setpoint within ten to fifteen minutes of a cold start. The stone is 3 to 7 kilograms of ceramic and it is still climbing.

So a stone in an oven that has just beeped is typically 100 to 150 F below the air around it. Launch onto that and the base steams instead of searing, which is the whole disappointing-first-pizza experience.

How to know rather than estimate

Point an infrared thermometer at the stone. Two seconds, and it replaces every model on this page with a number from your own oven.

Set the emissivity around 0.90 to 0.95 for a ceramic stone. On a steel, set 0.70 to 0.80 - a fixed-0.95 instrument reads a seasoned steel 40 to 83 F low, which is covered in the thermometer roundup.

Target: 500 to 550 F on the surface for a domestic-oven pizza. If your oven cannot get the surface past about 450 F no matter how long you wait, the oven is running cold and no preheat will fix it.

Does a longer preheat keep helping?

Not past 99 percent, no. The surface asymptotes toward oven temperature and cannot exceed it. Two hours does nothing a 45-minute preheat did not already do.

What a longer preheat does buy, once you are past that point, is the oven walls and the air being fully saturated too - which slightly improves recovery between pizzas. That is a small effect and it is not worth an extra hour.

The energy cost of waiting properly is small - roughly 21 cents for a full hour on an electric oven at the current US average rate. Worked out in what preheating costs.