How to Convert 8-inch to 9-inch Cake Pan: The Step-by-Step Guide

You've found the perfect birthday cake recipe. The photos are stunning, the reviews are glowing, but there's one catch: The recipe calls for an 8-inch round pan, and you only have a 9-inch pan in your cupboard.

It's one of the most common baking dilemmas. Many home bakers might think, "It's just one inch difference, I'll just pour it in!"

But that single inch makes a surprisingly big difference. If you don't adjust your recipe, your 9-inch cake will be thin, flat, and likely overbaked.

Don't worry—converting an 8-inch recipe to a 9-inch pan is actually quite simple once you know the "magic ratio." This guide will walk you through exactly how to scale your ingredients and adjust your baking time for perfect results.

The "Magic Ratio" for 8-to-9 Inch Conversion

The short answer: Multiply your ingredients by 1.25x.

Why 1.25? It all comes down to geometry. While the diameter only increases by 1 inch (12.5%), the area and volume increase much more significantly.

Here's the math behind the magic:

• Area of an 8-inch pan: 3.14 × 4² ≈ 50 square inches
• Area of a 9-inch pan: 3.14 × 4.5² ≈ 64 square inches

When you divide 64 by 50, you get 1.28.

So, a 9-inch pan holds about 28% more batter than an 8-inch pan. For simplicity in the kitchen, we round this to 1.25x (or adding 1/4 extra). This is easy to calculate and close enough for almost all cake recipes.

Step-by-Step: How to Scale Your Recipe

Let's say your original 8-inch cake recipe calls for:

• 2 cups flour
• 1 cup sugar
• 4 eggs
• 1 cup milk

Here is how you would convert it for a 9-inch pan:

1. Eggs First (The Tricky Part)

Eggs are hard to split.

• If the recipe calls for 4 eggs: 4 × 1.25 = 5 eggs. Perfect!
• If the recipe calls for 3 eggs: 3 × 1.25 = 3.75. You can use 4 eggs (the cake will be slightly richer) or whisk the 4th egg and use only 3/4 of it.

2. Dry Ingredients

Multiply by 1.25 (or add 1/4).

• Flour: 2 cups × 1.25 = 2.5 cups (2 & 1/2 cups)
• Sugar: 1 cup × 1.25 = 1.25 cups (1 & 1/4 cups)

3. Liquids and Fats

Same rule applies.

• Milk: 1 cup × 1.25 = 1.25 cups (1 & 1/4 cups)

What If I Don't Scale the Ingredients?

Maybe you don't want to do the math, or you don't have extra ingredients. Can you still bake an 8-inch recipe in a 9-inch pan?

Yes, but you must adjust the baking time.

Because the same amount of batter is spreading across a wider area, your cake layer will be significantly thinner—about 20% shorter than intended.

Adjustments needed:

1. Reduce Baking Time: Check the cake 5-10 minutes earlier than the recipe says. A thinner cake bakes faster.

2. Watch for Doneness: The toothpick test is crucial here. Since the cake is thinner, it can dry out quickly if overbaked even by a few minutes.

The Reverse: Converting 9-inch to 8-inch

What if you have a 9-inch recipe but only an 8-inch pan?

• The Ratio: 0.8x (multiply ingredients by 0.8, or roughly 80%).
• The Danger: If you try to pour all the batter from a 9-inch recipe into an 8-inch pan, it will overflow in the oven.
• The Solution: If you don't want to scale down the math, simply fill your 8-inch pan only 2/3 full. Use the leftover batter to make a few cupcakes on the side!

Skip the Math with Our Calculator

Don't want to calculate 1.25x for every single ingredient? We built a tool that does it instantly.

Use our Bakevert Cake Pan Converter.

1. Select "Round" shape for both pans.

2. Enter "8" for the original size and "9" for the target size.

3. Enter your ingredients.

4. Get the exact new measurements instantly.

It's free, precise, and saves you from doing mental math with eggs and teaspoons!

FAQ

Can I use an 8-inch square pan instead of a 9-inch round one?

Actually, yes! An 8-inch square pan holds about 64 square inches of batter—almost exactly the same as a 9-inch round pan. You can usually swap these 1:1 without changing ingredient amounts.

Do I need to change the oven temperature?

Generally, no. Whether scaling up or down, keep the temperature the same (usually 350°F / 175°C). The primary adjustment is the baking time, especially if the batter depth changes.

Does this work for cheesecakes too?

Yes, the 1.25x ratio works for cheesecakes, brownies, and pies. However, for cheesecakes, using a slightly larger pan without scaling just results in a thinner cheesecake, which is often acceptable and just requires less baking time.