Roll Cake Tray Size Conversion: Amounts for 25, 28 and 30 cm Square Trays
Roll cake recipes call for things like "a 28 cm square tray" or "a 30 cm square roll cake tray," but the trays that come with ovens are rectangular and vary in size. Since a tray sponge needs to bake thin and even, you adjust the amounts to the tray's area. This article gives a chart of factors between trays, a conversion example, tips for baking in your oven's tray, and a guide to thicknesses that roll easily.
Convert between trays by the ratio of their areas
A roll cake sponge is usually spread about 1 cm thick and bakes to about 1.5 cm. You want the same thickness even with a different tray, so scale the amounts by the ratio of tray areas (length × width).
Even a slight difference in tray area changes the thickness if you bake the same amount. Pour a 28 cm square recipe into a 30 cm square tray and the thickness falls to about 87%, so it's thin and prone to cracking when rolled. Pour it into a smaller tray and it gets thicker, harder to roll and slower to bake through.
Factors by tray size
Rows are the recipe's tray and columns are the tray you're using.
| Recipe \ Your tray | 25 cm square | 27 cm square | 28 cm square | 30 cm square | 30×24 cm |
|---|---|---|---|---|---|
| 25 cm square | 1 | 1.17 | 1.25 | 1.44 | 1.15 |
| 27 cm square | 0.86 | 1 | 1.08 | 1.23 | 0.99 |
| 28 cm square | 0.8 | 0.93 | 1 | 1.15 | 0.92 |
| 30 cm square | 0.69 | 0.81 | 0.87 | 1 | 0.8 |
- A 27 cm square and a 30×24 cm tray have almost the same area, so you can bake without changing the amounts.
- Baking a 28 cm square recipe in a 25 cm square tray is ×0.8, a difference of about 4 eggs versus 3.2.
- Larger oven trays such as 36×28 cm are about ×1.29 compared with a 28 cm square.
Converting a 28 cm square recipe
As an example, take a 28 cm square tray recipe with 4 eggs, 70 g granulated sugar, 40 g cake flour, 20 mL milk, 10 g butter and 200 mL fresh cream.
| Ingredient | 28 cm square (original) | 25 cm square (×0.8) | 30×24 cm (×0.92) | 30 cm square (×1.15) |
|---|---|---|---|---|
| Eggs | 4 | 3.2 (about 159 g) | 3.7 (about 184 g) | 4.6 (about 230 g) |
| Granulated sugar | 70 g | 56 g | 64 g | 80 g |
| Cake flour | 40 g | 32 g | 37 g | 46 g |
| Milk | 20 mL | 16 mL | 18 mL | 23 mL |
| Butter | 10 g | 8 g | 9.2 g | 11 g |
| Fresh cream | 200 mL | 159 mL | 184 mL | 230 mL |
Weighing beaten egg in grams is the reliable way. Cream is sold in 200 mL cartons, so if using a whole carton means a bit extra, that's fine, since a larger amount whips more easily. How to weigh eggs is covered in more detail in Cake Pan Size Conversion.
Tips for baking in your oven's tray
- 1
Measure the inside
Supplied trays often have rounded corners and sloping edges, so measure the length and width of the flat part of the base.
- 2
Make a paper mold
If the tray is too big, fold parchment paper into a slightly smaller box and calculate from its inside dimensions. Placing rolled-up aluminum foil along the outside of the paper mold keeps its shape.
- 3
Spread evenly into the corners
Pour the batter in the center, spread it to the corners with a scraper, then level the top. Uneven thickness causes uneven baking and cracks when rolling.
- 4
Bake hot and short
180–200 °C for 10–13 minutes is a guide. Overbaking dries the sponge and it cracks when rolled, so take it out when the top springs back to a light press.
How to roll without cracks
- As soon as it's baked, take it off the tray and cover with plastic wrap or parchment to cool so it doesn't dry out.
- Cut the far edge, where the roll ends, thin at an angle so the seam blends in.
- Make about 3 shallow cuts at 1–2 cm intervals along the near edge to help the core roll neatly.
- Spread cream thick where you start and thin where you finish, so it doesn't squeeze out when rolled.
- After rolling, wrap in plastic and chill for at least 1 hour. The shape settles and it slices more easily.
When the tray size changes, the length (one side of the tray) and thickness of the roll change too. A 30 cm square gives a length of about 30 cm, which yields 8–10 thick slices.
Baking a tray recipe in a square pan
If you have no roll cake tray, you can bake a thin layer of batter in a deep square pan. Here too, for the same thickness, convert by the ratio of areas.
| Pan | Area | Ratio to a 28 cm square tray |
|---|---|---|
| 18 cm square pan | 324 cm² | About ×0.41 |
| 20 cm square pan | 400 cm² | About ×0.51 |
| 21 cm square pan | 441 cm² | About ×0.56 |
A 20 cm square pan takes almost half of a 28 cm square recipe, or 2 eggs' worth. It rolls into a short cake about 20 cm long, just right for 2–4 people. Square pans have high sides that make it harder for heat to circulate, so bake a little longer than on a tray and check the springiness.
FAQ
- How do I make a 28 cm square roll cake recipe on a 30 cm square tray?
- Multiply by about 1.15. A 4-egg recipe becomes 4.6 eggs (about 230 g of beaten egg), and 70 g of granulated sugar becomes about 80 g.
- How many eggs for a roll cake on a 25 cm square tray?
- For a 28 cm square recipe with 4 eggs, 25 cm square is about ×0.8, or 3.2 eggs (about 160 g). For a 30 cm square recipe with 5 eggs, it's ×0.69, or about 3.5 eggs.
- Can I bake a roll cake on my oven's supplied tray?
- Yes. Measure the inside of the flat part of the base and convert by area. A 30×24 cm tray takes about ×0.92 of a 28 cm square recipe, and almost the same amounts as a 27 cm square recipe.
- How thick should roll cake batter be spread?
- About 1 cm before baking and about 1.5 cm after is a thickness that rolls easily. Scaling the amounts to the tray's area keeps this thickness.
Tools in this article
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