How Long To Bake 12×18 Sheet Cake

How Long To Bake 12x18 Sheet Cake

Baking a 12×18 sheet cake is a straightforward process that requires some understanding of the cake’s dimensions and its baking and decorating needs. This cake size is ideal for large gatherings, serving between 50-70 people, and is popular for various events, such as birthdays, weddings, and graduations.

This article will provide an in-depth guide on How Long To Bake 12×18 Sheet Cake, how to know when it’s perfectly baked, the ideal oven temperature, and how to serve and store it. We’ll also include some creative tips for decorating your sheet cake to make it the centerpiece of your gathering.

What is 12×18 Sheet Cake?

A 12×18 sheet cake is a rectangular cake that is baked in a sheet pan that is 12 inches by 18 inches. Some key things to know about 12×18 sheet cakes:

  • Size – The 12×18 size refers to the dimensions of the baking pan, so the cake itself will be approximately 12 inches wide by 18 inches long once baked and trimmed.
  • Number of servings – A cake this size will typically serve around 50-70 people depending on the portion size. It’s well suited for large gatherings and parties.
  • Uses – Sheet cakes are popular for birthday parties, weddings, graduations, and other celebrations. Their simple rectangular shape makes them easy to customize with decorations and lettering.
  • Baking process – Sheet cakes take less time to bake than round layered cakes since they are only 1-2 inches tall. They bake up with a flat, even surface that lends itself well to decorative icing.
  • Decorations – Sheet cakes are usually simply frosted on top, but can be decorated with piped borders, flowers, fondant accents, etc. Their large flat surface provides a good canvas for creative decorating.

So in summary, a 12×18 sheet cake provides a large, rectangular surface for feeding big crowds and decorating for special events. Its simple shape and large size make it useful for all kinds of gatherings.

How Long To Bake 12x18 Sheet Cake
How Long To Bake 12×18 Sheet Cake

Is a 12×18 a full sheet cake?

No, a 12×18 cake is not considered a full sheet cake. Here are the standard cake pan sizes:

  • Full Sheet Cake Pan: 18×26 inches
  • Half Sheet Cake Pan: 18×13 inches
  • Quarter Sheet Cake Pan: 13×9 inches

A 12×18 cake pan is larger than a quarter sheet but smaller than a half sheet. It’s sometimes called a “third sheet” cake pan. The full sheet cake pan at 18×26 inches is the largest standard rectangular cake pan size. Anything smaller than a full sheet is considered a “sheet cake” but not a full sheet.

How To Prepare 12×18 Sheet Cake?

This easy recipe for a 12×18 sheet cake is perfect for large parties and gatherings. By using two boxes of cake mix and baking in a large sheet pan, you can quickly make a cake that can serve up to 50 people. Simply mix, pour, bake, frost, and decorate – no special skills or fancy equipment required. With just a few basic ingredients, you’ll have a tasty homemade sheet cake ready to serve in no time.


  • Cake mix of your choice (enough to make 2 9×13 cakes)
  • Eggs, oil, and water as required by cake mix instructions
  • Frosting of your choice


How Long To Bake 12x18 Sheet Cake
How Long To Bake 12×18 Sheet Cake
  1. Pre-heat oven to temperature listed on cake mix box. Grease and flour a 12×18 inch sheet pan and set aside.
  2. Make the cake batter according to package instructions. This will require 2 boxes of cake mix to fill the 12×18 pan.
  3. Pour the batter evenly into the prepared sheet pan. Use a spatula to spread it into an even layer.
  4. Bake for 18-22 minutes or until a toothpick inserted in the center comes out clean. Baking time may vary based on your oven.
  5. Allow cake to cool completely in the pan on a wire rack.
  6. Once cooled, use a long serrated knife to evenly cut the cake horizontally into 2 layers.
  7. Place one layer on your cake platter or cardboard. Spread with frosting in an even layer. Top with second cake layer.
  8. Frost the top and sides of the cake with remaining frosting. Decorate edges with piped frosting if desired.
  9. Refrigerate cake for 30 minutes before serving to allow frosting to set. Store leftover cake covered in refrigerator.

Enjoy your homemade 12×18 sheet cake! The large pan size makes it perfect for big parties and events.

How Long To Bake 12×18 Sheet Cake?

A 12×18 sheet cake will need 30-40 minutes of baking time. Dense cakes like chocolate or carrot should bake 35-40 minutes. Lighter cakes like white or yellow cake need 30-35 minutes. Test for doneness with a toothpick – when it comes out clean, the cake is done. Watch closely towards the end of baking time. Allow the large sheet cake to cool completely in the pan before frosting and cutting for best results.

Read more: How Long To Bake A 11x15x2 Cake

How do I know when a 12×18 Sheet Cake is done baking?

Knowing when a sheet cake is fully baked can be tricky, but there are several ways to test for doneness. First, insert a toothpick or skewer into the center of the cake – when it comes out clean with no batter sticking to it, that’s a good sign it’s finished baking.

You can also gently press the top of the cake to see if it springs back – if it leaves an indentation, it needs more time.

Checking the sides of the cake and looking for it to pull away from the edges of the pan is another visual test, as is the cake developing a nice even golden brown color on top.

About 30-40 minutes is typical for a 12×18 sheet cake to bake at 350°F, so start checking it around the 30 minute mark.

Gently shake the pan and make sure the cake is set and doesn’t jiggle in the middle. And of course, the tried and true method is to simply smell the cake through the oven – you’ll know it’s nearly done when that homemade cake aroma wafts out. Use all of your senses and you’ll know when your sheet cake is perfectly baked.

How Long To Bake 12x18 Sheet Cake
How Long To Bake 12×18 Sheet Cake

What temperature should I bake an 12×18 Sheet Cake at?

For a standard 12×18 sheet cake, it is usually best to bake it at around 350 degrees Fahrenheit. This temperature allows the cake to bake evenly throughout without over-browning the outside. Baking at 350 degrees will ensure the inside cooks through while the outside remains lightly golden brown. Monitor doneness by inserting a toothpick – if it comes out clean, the cake is finished baking. Allow it to cool completely before frosting or decorating.

What to Serve and store 12×18 Sheet Cake?

A 12×18 sheet cake is a large cake that can serve a big group of people. When serving the cake, it’s best to cut it into rectangular slices so you get nice even pieces. Use a sharp knife to cut all the way through the cake and wipe the knife clean between cuts for neat slices. Plan for each person to get one modestly sized piece of cake – a cake this size when cut into 48 pieces will serve about 50 people.

For storing leftover sheet cake, cover it tightly in plastic wrap or foil and keep refrigerated. Make sure the cake is completely cooled before refrigerating. Leftover sheet cake will last 3-4 days refrigerated. You can also freeze the cake for longer term storage. Wrap it well in a few layers of plastic wrap and foil and freeze for up to 2-3 months. When ready to serve, thaw the frozen cake overnight in the refrigerator before unwrapping and cutting into slices. With proper storage, you can enjoy sheet cake for several days after the initial serving.

Tips to Decorating Ideas 12×18 Sheet Cake

  • Use a crumb coat. Apply a thin layer of frosting first to seal in crumbs. Chill in the fridge, then frost the cake completely. This gives you a smooth surface to decorate.
  • Stack cake tiers for more visual interest. Bake sheet cakes in different shapes and sizes, then stack them on top of each other with frosting or columns between layers.
  • Cover the cake in fondant for a smooth decorating surface. Roll out fondant and carefully lay it over the frosted cake. Smooth and trim excess. Fondant can be painted or airbrushed easily.
  • Add patterns with piping. Use piping tips to create swirls, dots, flowers, etc. Practice piping designs on parchment first. Use piping gel for sticky surfaces.
  • Arrange fresh fruit or berries on top into shapes or wreaths. Slice fruit thinly and fan out apples or pears.
  • Press edible sequins or confetti into the frosting. Purchase edible cake décor or make your own by printing out designs on edible paper.
  • Create an ombre effect. Tint frosting different colors and blend together with a spatula on the surface.
  • Use chocolate molds. Press chocolate shapes or letters into the sides of the cake for extra detail.
  • Add floral cake topper. Real or gumpaste flowers make an elegant topper. Arrange flowers crawling down the side for a cascading effect.
  • Incorporate a theme. Pick a motif like sports, nautical, seasonal, etc. and use themed decorations, colors, and designs.


A 12×18 sheet cake, often referred to as a “third sheet” cake, serves around 50-70 people, making it ideal for large gatherings. The baking process is relatively straightforward, requiring two boxes of cake mix for a pan of this size.

The cake typically takes around 30-40 minutes to bake at a temperature of 350 degrees Fahrenheit, with doneness confirmed by a clean toothpick test. Post-bake, cool it completely before frosting and cutting. When serving, cut it into rectangular slices, and store leftovers in the refrigerator, covered tightly for 3-4 days.

Further, this large, flat surface lends itself well to creative decoration, enabling you to customize it to suit any occasion or theme.


What temperature should I bake a 12×18 sheet cake at?
You’ll want to bake a sheet cake at around 350°F. This allows the inside to cook through while the outside bakes to a light golden brown. Baking at a higher temp risks over-browning the outside before the inside is done.

How can I tell when my 12×18 sheet cake is done baking?
Check for doneness by inserting a toothpick into the center. If it comes out clean with no batter stuck to it, the cake is finished baking. The edges should pull away slightly from the pan sides and the top should spring back when gently pressed.

How long does it take to bake a 12×18 sheet cake?
Baking times vary, but plan for around 30-40 minutes. Check at 30 minutes, then continue baking and checking every 5 minutes until a toothpick tests clean. The thickness and pan material impacts time as well.

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You can trust that you will receive honest and reliable information from our blog. As chef and blogger Amparo Zapata, I have over 8 years of experience as a Spanish chef. My role at Layla’s Authentic Spanish Restaurant and focus on our blog is to educate people about traditional Spanish cuisine. You can be confident that any recipes or cooking tips shared here are authentic and have been tried and tested in our restaurant kitchen. Our only goal is to spread the joy of Spanish home cooking and help you replicate the amazing flavors of Spain in your own home. I hope that through our blog, we can become a trusted resource for all things related to Spanish food.

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