Baking Pan Size Conversion
Scale a recipe from one baking pan to another by top area (round, square, rectangular), with the batter depth the full recipe would reach and the pan volumes.
The factor to scale the recipe by (new area ÷ old area), the depth a full recipe would reach in the new pan and whether it fits with room to rise, the two volumes, and a note on which way the baking time moves.
Example: A 9 in round (63.6 in²) to an 8 in square (64 in²) is × 1.006 — the same recipe; to a 20 cm round from a 33 × 23 cm sheet is × 0.41, so scale down or split the batter.
Batter spreads
to the footprint.
Why area is the right measure, what happens to depth when the recipe is not scaled, how volumes enter, and why baking time is only pointed at.
Area, not diameter
Batter spreads to the pan’s footprint, so a recipe developed for one pan fills another to the same depth when it is multiplied by the ratio of their top areas: πd²/4 for a round, side² or width × length otherwise. An 8 in round to a 9 in round is × 1.27, not × 1.125 — diameter misleads.
Depth and fit
Bake the recipe as written in a bigger pan and the batter is shallower by the same ratio; in a smaller pan, deeper. Enter the depth the batter reaches in the recipe pan and the page gives the new depth and, with the new pan’s height, whether it stays under three quarters full — most batters rise to that.
Time
A shallower layer bakes faster and a deeper one slower, but by how much depends on the batter; the page says which way, and the skewer test says when.
What the number does not settle
Loaf, tube and springform pans are their areas with the hole or well subtracted by hand; a dark pan and a glass one bake differently at the same size. Inputs stay in your browser; the same anonymous usage counts as the rest of the site apply.