Why did my cake overflow the tin?
A cake overflows for three separate reasons — too much batter for the tin, too much raising agent, or a tin that is the right width but the wrong depth. How to tell which, and what to do with the mess.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 5 min
Short answer
Fill a cake tin to about two-thirds of its depth and no more. If you filled it correctly and it still went over, the raising agent is the culprit — either too much was measured or a self-raising flour was used in a recipe that already added baking powder. Bake surplus batter as cupcakes rather than forcing it into one tin.
The two-thirds rule is about depth, not volume, and that is why people get caught out. A 20cm tin and an 18cm tin look similar on a shelf but the 20cm holds around a quarter more batter, so a recipe scaled for the larger one fills the smaller past the safe line before you have done anything wrong. A deep sandwich tin and a shallow one of the same diameter are further apart again. The drawing shows both fill levels in section and where the batter ends up.
What you'll need
- A tin of the size the recipe specifies (optional)
- A baking tray to stand the tin on
- Spare cupcake cases or a small tin for surplus batter (optional)
Step by step
- Deal with the oven first, before you diagnose anything.Burnt batter on the oven floor will smoke through the rest of the bake and set off the alarm. Slide a tray or a sheet of foil onto the shelf below to catch what is still dripping, and leave the cake in — opening the door for long enough to clean will sink it. Clean the floor once the oven is cold.
- Measure how full the tin actually was.You can usually see the batter line inside the tin once the cake is out. If it started above two-thirds of the tin's depth, that is your answer and the raising agent is innocent.
- Check the tin against the recipe.Measure the internal diameter across the base and the internal depth. A recipe written for a 20cm round tin overfills an 18cm round tin by roughly a quarter. Deep versus shallow sandwich tins differ by more again. See `convert-cake-tin-sizes` for scaling by area rather than by diameter.
- If the fill level was right, count the raising agents.The common error is self-raising flour used where the recipe called for plain flour plus baking powder, so the cake gets both. The other is a heaped teaspoon where a level one was meant. A sponge that rises violently, overflows and then sinks in the middle has almost always had too much lift.
- Look at what the overflowed cake did next.Batter that escaped took structure with it, so an overflowed cake is nearly always sunken as well. That sinking is a consequence, not a second fault — do not go looking for a separate cause.
- Next time, bake the surplus separately.Fill to two-thirds, put the rest into cupcake cases and bake them alongside for a much shorter time. This is always better than a tin that overflows and a cake that is raw where the batter sat too deep.
Tips
- Stand every cake tin on a baking tray as routine. It catches spills, evens out base heat, and makes a full tin far easier to carry to the oven.
- A batter that is loose and pourable rises and spreads more than a stiff one, so the same volume in the same tin is more likely to go over. Rich fruit cake batters can safely sit higher than a plain sponge.
- Springform tins leak batter at the seam as well as over the top. A loose base is a base, not a seal — line it and stand it on a tray.
- If you have deliberately scaled a recipe up, scale the tin by area rather than diameter or you will overfill by more than you expect.
Common mistakes
- Opening the oven mid-bake to mop up the spill — You will sink the cake to save the oven floor. A tray on the shelf below deals with the drips, and the floor cleans just as easily when cold.
- Assuming any tin of the right diameter will do — Depth varies by a factor of two between sandwich tins and deep tins of the same width. Depth is what decides whether two-thirds is reached.
If it doesn't work
Batter over the rim, cake risen high then collapsed into a crater
Cause: Too much raising agent, or self-raising flour plus added baking powder. The batter inflated faster than the crumb could set. — Fix: Remake with a level measure of a single raising agent. Check whether your flour is self-raising before adding anything to it.
Batter over the rim, cake otherwise a normal shape
Cause: Simply too much mixture for the tin — usually a tin one size smaller than the recipe assumed. — Fix: Fill to two-thirds and bake the remainder as cupcakes. If you regularly use a smaller tin, scale the recipe by area.
Overflowed and the centre is raw
Cause: The batter sat far deeper than the recipe's baking time was written for, so the outside set long before heat reached the middle. — Fix: Lower the temperature by 10–20°C and extend the time, or split the batter across two tins. See `fix-a-cake-burnt-outside-raw-inside`.
Only a loaf cake does it, round cakes are fine
Cause: Loaf tins are deep and narrow, so batter that looks modest is well past two-thirds of the depth once poured. — Fix: Judge by the depth line inside the tin, not by how much mixture is left in the bowl.
Questions people ask
Is two-thirds a hard rule?
It is a safe default rather than a law. Rich fruit cakes and dense batters with little raising agent can go to three-quarters because they rise very little. Whisked sponges, cakes with a lot of baking powder, and anything with bicarbonate reacting against an acid should stay at two-thirds or a shade under.
Can I still eat a cake that overflowed?
Yes, if it cooked through. Trim the burnt overflow lip off with a serrated knife and check the middle with a skewer. If the middle is raw as well, see `rebake-an-underdone-cake` before writing it off.