Cake Calculator
Calculate ingredients, servings, and baking times for any cake tin size
Serving Size Guide
Different occasions call for different portion sizes. Choose the right serving size for your celebration:
Party Portions
Larger slices (2.5cm x 5cm)
Perfect for birthdays, casual gatherings, and children’s parties where guests expect generous servings.
Wedding Portions
Smaller slices (2.5cm x 2.5cm)
Ideal for formal events, weddings, and occasions where cake is served alongside other desserts.
Afternoon Tea
Petite slices (2cm x 2.5cm)
Best for events with multiple sweet treats, afternoon tea parties, or tasting menus.
| Tin Size | Round Party | Round Wedding | Square Party | Square Wedding |
|---|---|---|---|---|
| 15cm (6″) | 10-12 | 12-14 | 16-18 | 18-20 |
| 20cm (8″) | 20-24 | 24-28 | 30-35 | 35-40 |
| 25cm (10″) | 32-38 | 38-45 | 48-55 | 55-65 |
| 30cm (12″) | 48-56 | 56-65 | 70-80 | 80-95 |
Baking Guidelines
Temperature Settings
Fan Oven
160°C (140°C for fan-assisted)
Reduce temperature by 20°C if using a fan oven. The circulating air cooks more efficiently.
Conventional Oven
180°C (Gas Mark 4)
Standard temperature for most sponge cakes. Always preheat your oven for at least 15 minutes.
Aga Oven
Baking oven (middle position)
Place cake in the centre of the baking oven. Check 5 minutes earlier than suggested time.
Baking Times by Tin Size
| Tin Size | Standard Depth (5cm) | Deep Tin (7.5cm) | Check After |
|---|---|---|---|
| 15cm (6″) | 20-25 minutes | 35-40 minutes | 18 minutes |
| 20cm (8″) | 25-30 minutes | 40-45 minutes | 22 minutes |
| 25cm (10″) | 30-35 minutes | 45-50 minutes | 28 minutes |
| 30cm (12″) | 35-40 minutes | 50-55 minutes | 32 minutes |
Recipe Scaling Method
The calculator uses volume-based scaling to determine ingredient quantities. Here’s how it works:
225g self-raising flour, 225g caster sugar, 225g butter, 4 eggs, 1 tsp baking powder, 2 tsp vanilla extract, 2 tbsp milk
Calculation Steps
1. Calculate Tin Volume
Round: π × radius² × depth
Square: side × side × depth
Rectangular: length × width × depth
2. Find Scaling Factor
Divide your tin volume by the base recipe volume (20cm round = 628 cm³)
Multiply this by the number of layers you want
3. Scale Ingredients
Multiply each base ingredient by your scaling factor
Round eggs to the nearest whole number
Adjust liquid ingredients slightly if needed for consistency
Frequently Asked Questions
Can I convert inches to centimetres?
Yes, multiply your inch measurement by 2.54. For example, a 6-inch tin is 15cm, an 8-inch tin is 20cm, and a 10-inch tin is 25cm.
Should I use salted or unsalted butter?
Unsalted butter is preferred as it gives you better control over the cake’s flavour. However, salted butter works perfectly well and can help balance the sweetness. Reduce added salt by half if using salted butter.
What if I only have plain flour?
Add 2 teaspoons of baking powder for every 150g of plain flour to substitute for self-raising flour. Sift together thoroughly before use.
Can I bake multiple layers in one deep tin?
Yes, but baking time increases significantly. A double-depth cake requires 45-55 minutes at 160°C. Check regularly after 40 minutes and reduce temperature to 150°C if browning too quickly.
How far in advance can I bake?
Un-iced sponge cakes keep well for 2-3 days in an airtight container at room temperature. For longer storage, freeze wrapped in cling film for up to 3 months. Defrost completely before decorating.
Why did my cake sink in the middle?
Common causes include: opening the oven door too early (wait at least 20 minutes), oven temperature too low, not enough raising agent, or overmixing the batter. Check your oven temperature with a thermometer.
Can I make this recipe dairy-free?
Yes, substitute with dairy-free margarine and plant-based milk (soya, oat, or almond work well). Ensure your margarine has at least 70% fat content for best results.
What size eggs should I use?
Medium eggs (53-63g) are standard for most recipes. Large eggs work too but may make the batter slightly wetter. Add an extra tablespoon of flour if using large eggs.
How do I ensure even baking?
Use quality tins with good heat distribution, position your oven shelf in the centre, rotate the cake halfway through baking, and consider using baking strips on larger tins to prevent doming.
Can I halve the recipe?
Yes, but you’ll need to deal with half eggs. Use 1 beaten egg and measure out half by volume, or freeze the leftover half egg for another use within 24 hours.
Ingredient Substitutions
| Original | Substitute | Notes |
|---|---|---|
| Caster Sugar | Granulated Sugar | Blend briefly for finer texture |
| Self-Raising Flour | Plain Flour + Baking Powder | Add 2 tsp per 150g flour |
| Butter | Margarine (70%+ fat) | Soften before use |
| Cow’s Milk | Oat/Soya Milk | Use unsweetened varieties |
| Vanilla Extract | Vanilla Bean Paste | Use same quantity |
| Medium Eggs | Large Eggs | Add 1 tbsp extra flour |
Common Baking Problems
Cake Too Dense
Causes: Overmixing after adding flour, too much liquid, insufficient raising agent, or eggs too cold.
Solutions: Mix flour gently until just combined, bring ingredients to room temperature, check raising agent expiry dates, and sift flour before use.
Cake Too Dry
Causes: Overbaking, not enough fat or liquid, oven temperature too high, or measuring flour incorrectly.
Solutions: Reduce baking time, add 1-2 tablespoons more milk, check oven temperature with thermometer, and spoon flour into measuring cup rather than scooping.
Uneven Rise
Causes: Uneven oven temperature, tin not level, or batter distributed unevenly.
Solutions: Rotate cake halfway through baking, use oven thermometer, level your oven shelf, and spread batter evenly with a spatula.
Cracked Top
Causes: Oven temperature too high, too much raising agent, or oven shelf positioned too high.
Solutions: Reduce temperature by 10°C, measure raising agent carefully, and move shelf to middle position.
Storage Recommendations
Room Temperature
Duration: 2-3 days
Store un-iced cakes in an airtight container. Iced cakes can be covered loosely. Keep away from direct sunlight and heat sources.
Refrigeration
Duration: 5-7 days
Best for cakes with fresh cream, buttercream, or cream cheese frosting. Bring to room temperature 30 minutes before serving for best flavour.
Freezing
Duration: Up to 3 months
Wrap unfrosted layers tightly in cling film, then foil. Label with date and size. Defrost overnight in fridge before decorating.
Buttercream Quantities
Calculate how much buttercream you need based on your cake size and decoration style:
| Cake Size | Filling Only | Filling + Crumb Coat | Full Coverage |
|---|---|---|---|
| 15cm (6″) 2 layers | 150g | 300g | 500g |
| 20cm (8″) 2 layers | 200g | 400g | 700g |
| 25cm (10″) 2 layers | 300g | 550g | 950g |
| 30cm (12″) 2 layers | 400g | 700g | 1200g |
250g unsalted butter (softened), 500g icing sugar (sifted), 2 tsp vanilla extract, 2-3 tbsp milk
Beat butter until pale and fluffy (3-4 minutes). Gradually add icing sugar, beating well. Add vanilla and milk until smooth and spreadable.
Tiered Cake Planning
Creating tiered cakes requires careful planning for both structure and servings:
Popular Tier Combinations
| Configuration | Serving Count | Best For |
|---|---|---|
| 15cm + 20cm | 35-45 people | Small weddings, anniversaries |
| 15cm + 20cm + 25cm | 70-90 people | Medium weddings, large parties |
| 20cm + 25cm + 30cm | 110-140 people | Large weddings, corporate events |
| 15cm + 20cm + 25cm + 30cm | 150-190 people | Very large celebrations |
Flavour Variations
Chocolate
Replace 50g flour with cocoa powder per 200g flour. Add 1 tbsp extra milk. Use same quantities calculated.
Lemon
Add zest of 2 lemons to batter. Replace vanilla with lemon extract. Consider lemon curd filling between layers.
Coffee
Dissolve 2 tbsp instant coffee in the milk before adding. Pairs excellently with chocolate buttercream.
Almond
Replace 50g flour with ground almonds per 200g flour. Use almond extract instead of vanilla. Check for nut allergies.
References
- NHS Eatwell Guide. (2024). “Sugar and the foods we eat.” Public Health England. Available at: https://www.nhs.uk/live-well/eat-well/
- Food Standards Agency. (2024). “Food allergen labelling and information requirements.” UK Government. Available at: https://www.food.gov.uk/
- British Baker Magazine. (2023). “Professional cake portioning standards for UK bakeries.” William Reed Ltd.
- Mary Berry. (2021). “Mary Berry’s Baking Bible.” BBC Books, London.
- Craft Guild of Chefs. (2024). “Industry standards for celebration cake sizing.” UK Professional Cookery Association.