Advanced options
Scaling is by tin area (same batter depth). Bigger, shallower cakes bake a little quicker; smaller, deeper ones need longer at the same or slightly lower temperature. A square tin holds about a quarter more than the same-size round: the old rule "go down 2cm from round to square" comes from exactly this maths.
What The Cake Tin Conversion Calculator Works Out
- Scale every ingredient by: the ratio of your tin's area to the recipe tin's area, which keeps the batter depth the same. A round tin's area is pi x diameter squared / 4; a square tin's is the side squared. Moving a 20cm round recipe into a 23cm round means x1.32; into a 20cm square means x1.27.
- Example: 200g becomes: the multiplier applied to a 200g ingredient, so you can see the rounding at a glance. Baking powder and bicarbonate scale linearly like everything else, but strong flavours, salt and spices reward scaling slightly shy at large multiples.
- Baking adjustment: time and temperature respond to depth, not weight. The same batter deeper needs longer and sometimes 10 degrees lower; shallower bakes faster; the skewer test outranks any clock. A square tin holds about a quarter more than the same-size round, which is where the old rule "go down 2cm from round to square" comes from; an 18cm square and a 20cm round are near-identical.
- Rectangular tins (advanced): enter a second side for either tin to treat it as a rectangle (a 20 x 30cm traybake, a 2lb loaf tin at about 10 x 21cm), which is what most traybake and brownie conversions need.
- Number of tins (advanced): two 20cm sandwich tins have twice the area of one, so a recipe for one deep tin split into two layers scales by x2 on area, not x1.
- Scale by volume (advanced): loaf, bundt and deep fruit-cake tins convert better by volume than by area because their depths differ by design. Enter both depths and the multiplier includes the depth ratio; the batter-depth card then shows how much deeper or shallower the cake will sit.
- Eggs become (advanced): eggs are the awkward ingredient. A factor of 1.32 on a 3-egg cake wants 3.96 eggs, so the card rounds to the nearest half (beat an egg and use half) and shows the exact figure.
- Estimated baking time and tin capacity (advanced): a rough timing from the recipe time and the batter-depth change (20% deeper takes about 10% longer), with the skewer test starting well before. Capacity to the brim lets you check the scaled batter will fit with room to rise; fill tins no more than two-thirds.