Why this conversion is not obvious
A 9-inch round pan sounds bigger than an 8-inch square because 9 is more than 8. But area tells the real story: 63.6 versus 64 square inches. Round and square pans of similar nominal size hold nearly the same batter, which is why so many recipes swap them freely.
The formulas
Round area = π × (diameter ÷ 2)². Square area = side². To match areas, the equivalent square side is diameter × √π ÷ 2 ≈ diameter × 0.886, and the equivalent round diameter is side × 2 ÷ √π ≈ side × 1.128.
Practical pairs
- 8 in round ≈ 7 in square (50.3 vs 49 in²)
- 9 in round ≈ 8 in square (63.6 vs 64 in²)
- 10 in round ≈ 9 in square (78.5 vs 81 in²)
- 9 × 13 rectangle ≈ two 9 in rounds (117 vs 127 in²)
What still changes
Corners brown faster in a square pan and the centre sets differently. A square cake will have slightly drier corners; a round one bakes more evenly. Neither is wrong — plan the frosting or trim accordingly.
Frequently Asked Questions
What square pan replaces a 9-inch round?
An 8-inch square holds virtually the same volume.
Does shape affect baking time?
Slightly — square pans have more perimeter, so edges set a little faster. Check a few minutes early.
Can I use this for brownies?
Yes; brownie recipes are forgiving of shape, though corner pieces will be chewier.
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