Time doesn't scale the way ingredients do.

Of all the things that change when you scale a recipe, cooking time is the most misunderstood. People assume time scales with quantity — twice the food, twice the oven — and they end up with cookies that are still pale, or a roast that's pulled before the centre hits temperature. The reality is that cooking time scales with geometry, not mass. Three rules cover most of what a home cook will encounter.

Rule 1: linear scaling for liquids and braises

Soups, stocks, simmered sauces, and braises behave roughly linearly. The volume of liquid determines how long the heat takes to circulate through it; doubling the volume roughly doubles the time the burner needs to reduce or sustain a simmer. The formula:

new_time ≈ old_time × (new_quantity / old_quantity)

This is the closest cooking time gets to the intuition of “more = longer”. Even here, you should taste before you trust the math — bigger pots take longer to come back to a simmer after stirring, and reduction rates change with surface area.

Rule 2: cube-root scaling for thick bakes and roasts

Cakes, loaves, roasts, casseroles, anything thick and three-dimensional. Doubling the volume of a cake doesn't double the cooking time, because the heat reaches the centre by penetrating through the surface. A cube that's twice the volume is only about 1.26× wider on each side, so the heat only has 1.26× as far to travel. The formula:

new_time ≈ old_time × ∛(new_quantity / old_quantity)

For a 2× recipe, this gives roughly 25% longer; for a 4× recipe, roughly 60% longer. Always verify with a thermometer (74 °C / 165 °F for poultry; 60 °C / 140 °F for medium-rare beef) or a doneness check (a clean skewer for cake, a hollow knock for bread).

Rule 3: square-root scaling for sheet bakes

Cookies, sheet pans of brownies, focaccia in a half-sheet, anything thin spread over a broader surface. The depth doesn't change much when you scale; only the area does. The formula is conservative:

new_time ≈ old_time × √(new_quantity / old_quantity)

In practice, sheet bakes barely change. A doubled batch of cookies on the same pan depth bakes in approximately the same time — you're just running more sheet pans through the oven. The constraint is oven capacity, not time.

Why the formulas differ

Cooking time depends on heat reaching the centre of the food, not on the food's mass. For thin items, the centre is already close to the surface, so doubling the mass barely affects time. For thick items, doubling the mass increases the linear distance the heat needs to travel by the cube root of the volume change. For liquids, convection currents make the bulk heat up almost as quickly as the volume increases, so the relationship is closer to linear.

What the converter does and doesn't tell you

The widget at the top of this page gives all three estimates side by side. Pick the one that matches your dish's geometry and use it as a starting estimate— never as a definitive answer. The actual time depends on:

• Oven recovery: when you open the door to add more food, the temperature drops; bigger ovens recover faster.
• Pan conductivity: dark metal absorbs more heat than light metal, glass less than metal, ceramic least of all.
• Pan depth: a deeper pan with the same surface area (see the pan-size converter) takes longer to bake through.
• Starting temperature: a roast straight from the fridge cooks slower than one tempered for 30 minutes on the counter.

How to actually verify doneness

Because time is unreliable, the cooked-and-true methods are better. Buy a digital instant-read thermometer — it pays for itself the first time it tells you that yes, the chicken really is done. For baked goods, a wooden skewer in the centre that comes out clean (or with a couple of damp crumbs for moist cakes) is the gold standard. For bread, an internal temperature of 88–98 °C (190–210 °F) is doneness depending on the style.

Pairing with the scaler

The recipe scalerdeliberately doesn't adjust cooking time, because the right rule depends on the dish — and the algorithm shouldn't guess. Use this page to pick the rule that fits, then apply the estimate as a starting point. For pan changes that compound the time question, see the pan-size converter.