Baking pan converter: volumes, equivalents and recipe scaling
“My tin is 8-inch, not 9-inch” is the moment a bake gets decided. This tool does the three sums that fix it: volume from dimensions (so you know what the pan holds), equivalents by area (the King Arthur 9″-round ≈ 8″-square swap), and a scale factor with honest egg-rounding help. The methodology section shows the geometry and the published charts we checked it against.
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Key takeaways
- 9″ round ⇄ 8″ square is a direct swap — both 64 in² of base area (King Arthur Baking's published equivalence; our geometry gets 63.6 vs 64).
- Round pans are cylinders, tins are boxes: volume = πr²h or l×w×h; 1 cup = 240 ml = 14.4375 in³.
- Plan batter at ⅔ of brim volume — the standard fill rule; published “capacities” mix brim and usable figures (King Arthur: a 10-cup Bundt bakes ~6 cups).
- Scale by batter capacity, then fix the eggs — round scaled eggs to halves; a half egg ≈ 2 tbsp beaten.
- Batter depth drives doneness: same batter, deeper pan = longer bake, lower temp for loaves.
Methodology: geometry first, published charts second
Pan conversion is one of two honest approaches: look up a number somebody printed, or compute it. We compute, then sanity-check against the printed charts:
- Brim volume: round pans are cylinders (π × (d⁄2)² × h), rectangular pans and loaf tins are boxes (l × w × h), measured inside rim to inside rim. We convert cubic inches to cups at 1 cup = 240 ml = 14.4375 in³ — the same 240 ml conversion used by Sally's Baking Addiction's published pan-capacity chart.
- Batter capacity: brim × ⅔, the fill rule stated on that same chart (“filling pans around 2/3 full is the best practice”). This is the number that decides whether a recipe fits.
- Listed capacities vary by maker: King Arthur Baking notes that a “10-cup” Bundt is a brim listing whose practical baking capacity is about 6 cups. Our library therefore carries both the computed brim volume and the published figure, and every row agreed within ±20% when we checked (worst case: loaf tins, where published figures sit near the ⅔ line rather than the brim). See why volumes differ.
- Equivalents by area: for equal batter depth you need equal base area — square side = d × √π⁄2 ≈ 0.886 × d. That reproduces King Arthur's published example (9″ round ≈ 8″ square, 64 in²) to within 0.03″.
- Scaling: factor = target batter capacity ÷ recipe pan's batter capacity; factors within 0.9–1.1 are “bake as-is”. The full derivation with depth effects is in pan substitution math.
Last verified: 2026-11-16 — sources: Sally's Baking Addiction pan chart, King Arthur Baking pan guides (all fetched live on that date).
Worked examples
Example 1: brownie recipe for an 8″ square — you own a 9″ round
Swap mode, 8″ square → 9″ round: factor ×1.00 (5.92 vs 5.87 cups batter). Same area (64 in²), same depth, same bake time. This is the direct swap King Arthur publishes, confirmed by geometry.
Example 2: cake for two 8″ rounds — you own one 9″ round
Two 8×2 rounds hold ~11.8 cups batter; one 9×2 round holds ~5.9 cups. Factor ≈ 0.50: halve the recipe (3 eggs → 1½ — beat one extra egg, use 2 tbsp) or bake in two batches with an even split.
Example 3: loaf recipe for a 8½×4½ tin — you own 9×5
Factor ≈ ×1.16: make the recipe as written for a slightly shorter loaf, check 5 minutes early, or scale up by a sixth. The temperature-mistakes guide covers the deeper-tin temp drop (25°F/15°C for very deep bakes).
Parchment sheets sized for 8″ and 9″ pans
Pre-cut parchment beats scissors-and-curl every time — and swapping pan sizes hurts less when the liner already fits both.
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