Pan Size Converter

How the Pan Size Converter works

Capacity comes first. The footprint is π × radius² for a round pan, side² for a square, length × width for a rectangle or loaf tin, and for a bundt or tube pan the footprint is reduced by a quarter to account for the centre tube and fluting — the reason a 10-inch bundt doesn't hold what its diameter suggests. That footprint is multiplied by the pan's wall height and then by two-thirds, because batter needs headroom to rise and a pan filled to the rim is a pan that overflows onto the oven floor. The result is converted to US cups, which is a number you can sanity-check against a measuring jug.

The scale factor is then the ratio of those two capacities. If your pan holds 8 cups and the recipe's pan holds 12, scaling to 0.67× fills yours to the same depth the recipe author intended, which is the depth their bake time was written for.

Bake time is a separate calculation, and it is deliberately not driven by footprint. What sets how long a bake takes is how far the centre sits from the outside — the DEPTH of the batter — because that's the distance heat has to travel. Pour a 9-inch round's batter into a 9×13 and it spreads to roughly half the depth, so it sets considerably faster. The relationship is sub-linear rather than proportional (top and bottom surfaces don't move apart in step with the footprint), so the tool applies a 0.75 exponent to the depth change, which is a curve fit to the standard published rule of thumb rather than a law of physics.

Temperature is the last adjustment and only fires in one direction. If the batter ends up more than about 25% deeper than the recipe intended, the tool suggests dropping the oven 25°F — a deeper batter at the stated temperature sets its crust and browns its top well before the centre is done. A shallower batter needs no temperature change, just an earlier check.

Worked example: the recipe says 9×13 and you own one 9-inch round

A 9×13 pan with 2-inch walls holds about 10.8 cups of batter at a two-thirds fill; a 9-inch round with the same wall height holds about 5.9. Your pan takes a little over half of what the recipe's does, so the tool returns a scale factor of 0.54 and says plainly that the full recipe does not fit — pouring it in anyway is how batter ends up on the oven floor. Scale the ingredients to 0.54× with the Recipe Scaler, or bake the remainder as a few cupcakes. If you did pour the lot in, the batter would sit nearly twice as deep as intended, which is why the tool also asks you to drop the oven 25°F and expect around 58% more time.

Run it the other way and the second answer becomes the interesting one. You have the 9×13 and the recipe was written for the 9-inch round: the batter fits easily, but it spreads across nearly twice the footprint and sits at just over half the depth. The tool reports no scaling needed and roughly 37% off the bake time, with no temperature change — the failure mode here isn't overflow, it's walking away for the full stated time and coming back to something dry. An 8-inch square against a 9-inch round is the opposite case and the reassuring one: 5.9 cups against 5.9, near enough identical that the tool tells you bake time is effectively unchanged. That is why that particular swap is the one bakers already make without thinking, and it is a useful check that the model is not inventing differences.

Edge cases this tool handles correctly

Pans of the same footprint but different heights

Two 9-inch rounds with 2-inch and 3-inch walls have identical footprints and very different capacities, which is exactly the case a footprint-only chart gets wrong. Because this tool asks for wall height, it separates them — but note that if you don't fill the taller pan any deeper, the bake time doesn't change; only the amount you can fit does.

Bundt and tube pans

The centre tube is why a bundt pan bakes faster than its size suggests — it puts an extra heated surface in the middle of the batter, so the deepest point is much closer to a wall than in a solid pan. The tool discounts the footprint by 25% for capacity, but treat its time estimate as conservative for bundts: start checking earlier than it suggests.

The two-thirds fill assumption

Every capacity figure here assumes batter filled to two-thirds of the wall height, the standard published guidance for a rising cake. A dense batter that barely rises — a brownie, a cheesecake — can go fuller, so the tool will tell you a pan is too small when in practice it would have coped. The figures shown in cups let you make that call yourself rather than hiding the assumption.

Timing is a checking point, not a bake time

The percentage is where to start testing, not when to take it out. A skewer in the centre is the only real doneness test, and no geometry model substitutes for it — ovens vary by more than these adjustments do.

Frequently asked questions