THE GEOMETRY OF BAKING
A recipe is a blueprint, but the tin is the foundation. Changing the size or shape of your baking tin isn’t just about whether the batter fits; it’s about how heat travels through the shape, size and material of the pan.
When you swap a 20cm round tin for a 20cm square one, you aren’t just changing the corners, you are increasing the surface area by roughly 25%. This guide is designed to help you navigate those shifts with ease, ensuring your favorite bakes come out perfectly, regardless of the tin.
Baking is spatial geometry. When you change the shape, you change the way heat travels to the heart of the cake.
THE CORE PRINCIPLES OF VOLUME
Before you pour, consider these three rules for tin swapping:
- The Two-Thirds Rule: Regardless of the shape, never fill a tin more than two-thirds full. Batter needs room to climb; if it hits the ceiling too early, the structure will collapse.
- The Water Test: If you are unsure if a recipe will fit a new tin, fill your original tin with water, then pour that water into the new one. If it fills to the same level, you’re safe.
- Surface Area vs. Time: A shallower, wider tin bakes faster than a deep, narrow one. If you are spread thin, drop your temperature by 10∘C and start checking for doneness 10 minutes early.
Dane’s Tip: If you’re not sure if your batter will fit? Fill your tin with water using a measuring jug. If the tin holds 6 cups of water, it will safely hold 4 cups of batter (leaving room for the rise).
SHAPE SHIFTING: COMMON CONVERSIONS
Use these shortcuts to swap shapes without doing the long-form math.
Round to Square
Square tins hold more volume than round ones of the same “width.” To keep your cake height consistent, move down one size when switching to square.
- 15cm (6″) Round = 13cm (5″) Square
- 20cm (8″) Round = 18cm (7″) Square
- 23cm (9″) Round = 20cm (8″) Square
- 25cm (10″) Round = 23cm (9″) Square
The Loaf Tin Logic
A standard 22cm × 12cm loaf tin is a versatile beast.
- It is roughly equivalent to an 18cm Round tin or a 15cm Square tin.
- A standard loaf tin usually holds about 6 cups (1.5L) of batter.
- Note: Loaf tins are deeper; expect to increase your bake time by 10–15 minutes.
Muffin & Cupcake Swaps
- A standard 20cm (8″) Round cake recipe will typically yield 12 to 15 standard cupcakes.
- Bake cupcakes at the same temperature as the cake, but reduce the time to 18–22 minutes.
THE VOLUME REFERENCE MAP
Based on a standard depth of 5cm (2 inches).
| Tin Shape & Size | Approx. Volume (Cups) | Best Replacement |
| 15cm Round | 4 Cups | 1 loaf tin (22cm × 12cm) |
| 20cm Round | 8 Cups | 18cm Square tin |
| 23cm Round | 11 Cups | 20cm Square tin |
| 20cm Square | 10 Cups | 23cm Round tin |
| 23cm Square | 14 Cup | 33cm × 23cm Rectangular pan |
A NOTE ON MATERIAL
Dark vs. Light Tins The “Home Baker” needs to know that the finish of your tin matters as much as the size.
- Dark or Non-stick Tins: These absorb more heat. If your cake edges are burning before the middle is set, reduce your oven by another 10∘C.
- Professional Aluminium: This provides the most even heat distribution and is the gold standard of the Baker Gatherer kitchen.
Lining your baking tins
A perfectly converted recipe deserves a perfectly lined tin. If your baking paper isn’t flush against the sides of the pan, your cake will struggle to climb or, worse, develop “pleated” edges (Unless that’s your desired aesthetic).
The Round Tin: The “Fringe” Method
Don’t fight the curves. To get a seamless fit for round cakes:
- The Base: Trace the bottom of your tin onto baking paper and cut exactly inside the line.
- The Collar: Cut a long strip of baking paper slightly taller than the tin’s sides.
- The Fringe: Fold the bottom 1cm of that strip upward. Snip small “V” shapes into that folded edge every 2cm.
- The Install: Grease the tin, press the fringe into the bottom corner so it sits flat, and then drop your base circle on top to lock it in place.
The Square Tin: The “Cross” Method
Corners are the enemy of clean releases. Skip the folding and bunching:
- Cut two long strips of baking paper exactly the width of the tin’s base.
- Grease the tin and lay the first strip across, leaving “handles” hanging over two opposite sides.
- Lay the second strip perpendicular to the first.
- This creates a double-layered base and perfectly clean corners, with built-in handles to lift the bake out safely once cooled.
Dane’s Tip: Always grease the tin before the paper, and the paper before the batter (If you like). Double-greasing ensures the baking paper stays still while you spread the batter, and peels away like silk once baked.