Two 9-inch Rounds to 9×13 Rectangle:
The Nearly Perfect Match

9"
9"

Two layers

16 cups total

→
9×13"

Single layer

14.6 cups

×0.92

Use 92% of ingredients - almost the same!

✨ This is one of the easiest conversions!

The volumes are so close, you could even use 100% and just have a slightly taller cake

Why This Conversion Is Nearly Perfect

The Math Is Beautiful

Two 9" rounds:127 sq in
(2 × π × 4.5² = 127.23)
One 9×13":117 sq in
(9 × 13 = 117)
Only 8% difference!

Depth Comparison

Each 9" layer:

Usually 1.5-2" deep

9×13" result:

About 2" deep

✓ Almost identical depth!

Minimal Adjustments Needed

Same Temp

Keep at 350°F - no adjustment needed for this conversion

+5-10 Minutes

Single thick layer takes slightly longer than two thin ones

Watch Corners

Rectangle corners cook faster than round edges

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Pro Baker's Secret

"When converting from two 9-inch rounds to 9×13, I often just use the full recipe (100% instead of 92%). The extra 8% gives you a slightly taller cake that's perfect for sheet cakes. No one ever complains about a too-tall cake!"

The 100% Method:

  • • Use all the batter from the layer recipe
  • • Fill pan about 2/3 full (perfect!)
  • • Add 8-12 minutes to baking time
  • • Get a bakery-style tall sheet cake

Quick Conversion Examples

If Using 92% Scaling:

3 cups flour→ 2¾ cups
4 eggs→ 4 eggs (keep same)
1 cup butter→ ⅞ cup + 1 tbsp
2 cups sugar→ 1¾ cups + 2 tbsp

Or Just Use 100%:

Honestly? The 8% difference is so small, most bakers just use the full recipe:

  • ✓ No math needed
  • ✓ Slightly taller cake
  • ✓ More impressive presentation
  • ✓ Extra batter? Make a cupcake!

When to Use This Conversion

✅ Perfect For:

  • • Potlucks (easier transport)
  • • Picnics (no stacking issues)
  • • Kids' parties (easy squares)
  • • Freezing (flat storage)
  • • When you have one 9×13 pan

💡 Consider:

  • • Less frosting surface than layers
  • • No middle layer of filling
  • • Different presentation style
  • • May need moisture boost
  • • Corners vs. round edges

Related Pan Conversions

12-Cup Bundt → Two 9"

Bundt to layer cake

9×13" → Two 9"

Reverse conversion

Two 8" → 9×13"

Smaller rounds to sheet

9" Round → 9×13"

Single layer to sheet

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