Not sure how big your cake needs to be? This portion guide takes the guesswork out of ordering, so every guest gets a generous slice.
One of the most common questions I get asked is: what size cake do I need? Order too small and you run out of slices. Order too big and you are left with half a cake nobody takes home. Getting the size right saves you money and makes sure every guest at your birthday celebration gets a proper portion. Here is everything you need to know.
This table gives you a straightforward overview. Portions are based on standard party slices, which are slightly smaller than a full dessert serving.
| Number of Guests | Cake Size | Tiers | Approximate Portions |
|---|---|---|---|
| 5 to 10 | 6 inch round | Single | 10 to 12 party slices |
| 10 to 20 | 8 inch round | Single | 20 to 24 party slices |
| 20 to 30 | 10 inch round | Single | 28 to 30 party slices |
| 25 to 35 | 6 inch + 8 inch | Two tier | 30 to 36 party slices |
| 35 to 50 | 6 inch + 8 inch + 10 inch | Three tier | 50 to 60 party slices |
| 50 to 80 | 6 inch + 8 inch + 10 inch + 12 inch | Four tier | 80 to 100 party slices |
| 80+ | Tiered cake + sheet cake | Varies | 100+ party slices |
These numbers are guidelines. The exact portion count depends on how the cake is cut and whether you are serving it as a party snack or the main dessert. For a more detailed breakdown with diagrams and cutting guides, visit our complete cake portion guide.
This is a really important distinction that many people overlook. A party portion is a slim finger of cake, roughly 1 inch wide and 4 inches long. It is designed for celebrations where cake is just one of many things to eat. A dessert portion is a generous wedge, roughly 2 inches wide, and is meant for when the cake is the star of the show.
If your birthday party includes a full buffet or dinner before the cake, party portions will be more than enough. If the cake is the main event after a light spread of nibbles, go with dessert portions. As a rule of thumb, a cake that serves 30 in party portions will serve about 15 as a dessert.
My advice: when in doubt, go one size up. Leftover birthday cake is never a problem. Running out of cake always is!
The shape of your cake affects how many portions you get. Square cakes yield more slices than round cakes of the same measurement because there is more surface area.
| Cake Size | Round (Party Portions) | Square (Party Portions) |
|---|---|---|
| 6 inch | 10 to 12 | 14 to 18 |
| 8 inch | 20 to 24 | 28 to 32 |
| 10 inch | 28 to 30 | 40 to 50 |
| 12 inch | 40 to 48 | 56 to 72 |
If you are hosting a larger gathering and want to keep costs manageable, a square cake can be a smart choice. You get significantly more portions from the same tier size, which means you may be able to go with fewer tiers.
For large birthday parties with 50 or more guests, here is a trick that professional bakers and event planners use all the time: order a smaller, beautifully decorated display cake for the table and a plain sheet cake to be kept in the kitchen for cutting.
The display cake is what the birthday person blows out their candles on. It is the one that appears in all the photos. The sheet cake provides the bulk of the portions at a fraction of the cost of making every slice from an elaborately decorated multi tier cake.
This approach lets you have a stunning centrepiece without paying for 100 portions of a fully decorated cake. A matching sheet cake in the same flavour typically costs £40 to £70 depending on size and can add 30 to 60 extra portions. If you want to explore what this might cost overall, our guide to birthday cake prices in London has a full breakdown.
Not every celebration needs a traditional tiered cake. Cupcakes are a brilliant alternative for several situations:
A popular option is to combine a small 6 inch cake for the candle moment with a batch of matching cupcakes for the guests. This gives you the best of both worlds: a beautiful cake for photos and easy individual portions for everyone else.
If you want to make a real statement at your birthday party, consider a full dessert table. A dessert table typically features a centrepiece cake surrounded by complementary treats like cupcakes, cake pops, macarons, brownies and biscuits. Everything is colour coordinated and styled to match your party theme.
Dessert tables are particularly popular for milestone birthdays like 40th and 50th celebrations, where the birthday person wants something extra special. Because you are spreading portions across multiple treats, the centrepiece cake can be smaller and more detailed, which often saves money compared to a single massive tiered cake.
A 6 inch or 8 inch single tier cake is perfect. Keep it simple but beautiful. This size works brilliantly for family dinners and small at home celebrations. If you are after design inspiration, our guide to birthday cake ideas is full of styles that look stunning at any size.
A two tier cake is your best bet. The combination of a 6 inch tier on top of an 8 inch tier comfortably serves 30 to 36 guests and creates an impressive visual impact. For parties closer to 40, consider adding cupcakes or a small sheet cake to supplement.
Go with a three or four tier display cake plus a sheet cake. This is the most cost effective way to serve a large group while still having a showstopper centrepiece. Many of our clients who book celebration cakes for large events use this combination.
Every party is different, and there is no single formula that works for everyone. The best thing to do is send me a quick message with how many guests you are expecting, the type of celebration and your budget. I will recommend the perfect size and style to suit your needs. Do not forget to read our ordering timeline guide so you know exactly when to get in touch.
Tell Paulina how many guests you are expecting and she will recommend the perfect size, shape and style for your celebration.
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