Brownie Pan Size Calculator

Brownies, blondies, and bar cookies spread to fill the pan. The batter depth is what sets the bake time and the texture, and depth is just batter volume divided by pan area.

When you switch pan sizes, you scale all ingredients by the area ratio. If the new pan has 1.83 times the area of the old pan, you need 1.83x as much of every ingredient.

Scaling factor = new pan area / original pan area

Common pan areas (inches squared):

• 6x6: 36 sq in (the smallest common size, right for a half batch)
• 8x8: 64 sq in (the classic brownie pan)
• 8-inch round: 50 sq in
• 9-inch round: 63.6 sq in (near enough an 8x8, which is the useful accident here)
• 9x9: 81 sq in
• 7x11: 77 sq in
• 8x12: 96 sq in
• 9x13: 117 sq in (standard sheet cake pan)
• 11x15: 165 sq in (jelly-roll pan)
• 13x18: 234 sq in (true half-sheet)

That round-pan coincidence is worth remembering. A 9-inch round cake pan comes within half a percent of an 8x8 square, so you can bake an 8x8 brownie recipe in one with no adjustment worth making. An 8-inch round is about 21% smaller and will give you noticeably thicker, gooier bars.

When you scale the recipe proportionally, the batter depth in the new pan stays about the same as in the original, so baking time should be similar. The main exception: if you end up with a much shallower or deeper layer than intended, adjust by 5-10 minutes and use a toothpick test.

What if you do not scale the recipe?

This is what most people actually do. They pour an 8x8 recipe into the 9x13 because it is the pan that was clean. The batter then spreads over 1.83 times the area, so the layer comes out 45% thinner and bakes much faster. The calculator reports the depth change and an earliest sensible check time, which is the original time cut in the same proportion as the depth. A thinner layer is never going to take longer, so that figure is a floor rather than a prediction. Start checking there.

Thin brownies also change character, not just timing. Under about 1/2 inch you are making a chewy bar rather than a fudgy one, and the middle sets before it ever gets gooey.

Temperature stays the same regardless of pan size.

A practical tip: if you are scaling up for a crowd, the 9x13 is almost exactly 1.83x the 8x8. So an 8x8 recipe that calls for 2 eggs becomes 3.66 eggs. Round to 4 and accept that the 9x13 batch will be very slightly richer.

Glass pans hold heat and keep cooking after you pull them, so drop the oven 25°F and check early. Silicone is the opposite problem: it insulates rather than conducting, so keep the temperature the same and expect to add a few minutes, with pale edges and no crust where the batter touches the mold.