How pan size converter works
Every pan-substitution question is an area question. A round pan's cooking surface is π × (diameter ÷ 2)², a square's is side × side, and a rectangle or loaf's is width × length. The conversion factor is simply the target pan's area divided by the original's — an 8-inch round (50.3 in²) into a 9-inch round (63.6 in²) is a factor of 1.26, so every ingredient gets multiplied by 1.26.
Depth matters when the pans are not equally deep. With depths entered, the tool computes true volumes (area × depth, with 1 US cup = 14.4375 in³) and scales by volume instead of area — the right answer for loaf pans, which are deep and small-footprint, versus shallow sheet-style pans of the same footprint.
The factor adjusts quantities, not time. A larger pan spreads the same batter thinner, so it bakes faster; a smaller, deeper pan takes longer and can sink in the middle if the center stays wet. That is why the result includes a baking-time hint: keep the oven temperature, start checking early on bigger pans, and expect extra minutes on smaller ones.
Two practical guardrails come free with the math: never fill a pan more than about two-thirds to three-quarters full (batter rises), and when the factor lands between 0.9 and 1.1, the pans are close enough that most recipes survive unchanged — check doneness a few minutes early either way. Odd shapes like Bundt tins are not modeled here because their tube and flutes put area and volume out of proportion; scale those by water volume instead.