OK, we’re going to talk about math today, and how to make half-sheet pan-sized (13″ x 18″) batches of your favorite 9″ x 13″ recipes.

Before you get too freaked out, let’s just start with **the most correct answer: 1.5.**

Back in the day, when I was in high school, my intellectual bent had way more to do with artistic seethings than anything mathematical. It wasn’t until culinary school (that OTHER CIA, in Hyde Park, NY) that math made any sense to me.

There’s plenty of math in baking. I use conversion factors more than anything else. Say you have a cookie recipe that makes 3 dozen cookies, but you need more cookies than that. Double everything, and you’ve multiplied all the ingredients by a conversion factor of 2. Simple.

Or, you’re a small household, and really don’t want to stare down a 9″ x 13″ pan of brownies for two weeks. You can cut the recipe in half, and bake it in an 8″ square pan. The conversion factor there is .5. How did I know what size pan to bake in? I compared the bottom surface area of the pans involved. Take a look:

The 8″ square pan has 79% of the area of the 9″ square pan, and slightly more than half the area of the 9″ x 13″ pan.

As long as you’re staying within 10% of the area the recipe was designed for, you can move back and forth between them. Now for the exception to what I just told you.

It would seem like a no-brainer that doubling a 9″ x 13″ recipe would be perfect in a 13″ x 18″ half-sheet pan. After all, 117 x 2 = 234 exactly. All the beauty and perfection that is mathematics says it should work, but there’s one hitch.

The sides of the pan. All the other conversions we spoke of involve pans whose sides are at least 2″ tall. The sides of a half-sheet pan are only 1″ tall. At this point, it’s time to introduce a third dimension (height) to our calculations, and that means we’re talking about the recipe’s volume, not just the area of the pan’s bottom.

Leaving a perfectly innocent-looking pan with a double batch of cake in it…

…to perform the slow, hypnotic, lava-like overflow.

Believe you me, I learned this one the hard way – with brownies, which are much more of a Kilauea experience. They just keep overflowing… and overflowing… and… The scent of burning chocolate and sugar rolls through the house (or test kitchen), as the shame washes over in waves. You don’t want to go there.

Which brings me back to the answer: **1.5**. For more portions with the same amount of work, remember one and a half times any 9″ x 13″ recipe will give you a half-sheet pan’s worth of product. If you’re baking for a church supper, a bake sale, a big family gathering, or your local firehouse, it’s a very handy thing to know.

Some suggestions to get you started: Butterscotch Finger Cakes(the cake I worked with up above) Old-Fashioned Apple Cake, our favorite Brownies; or some Sticky Ginger Squares (great for holiday giving).

Useful info on increasing a recipe for a half-sheet pan. But, there are some problems in the section on 8″ and 9″ square pans. A 9″ square pan is 81 square inches, 9×9=81, not 91. So, an 8×8 pan has 79% of the area of a 9″ square, not 70%.

Also correct. Remember my caption about writing poems on my math tests? Will go correct right away. Thank you. SusanA 9 inch square pan is 81 square inches, not 91 square inches.

You are absolutely correct. Thanks, Margaret.

To scale for a 3/4 sheet pan, would I then double the 9 x 13? That would give me 234, which represents .66% of the 352 sq. inches of a 3/4 sheet pan.

Hi, Jen. I think that’s worth a try, depending on the recipe. Just to be sure, put something on the rack underneath to catch any drips. SusanThanks for the lesson…….Think I’ll have to reread it sometime after I’ve had more coffee and the brain cells seem to be working…….Middle-age……What can you do about it….teehee

Agreed, waikikirie. Too much math too early is painful. 🙂 SusanOh, Susan, a post about my favorite pan ..thank you!

My half sheet is well-travelled, with Buffalo chic pizza going to youth group parties and big apple crisps to the potluck.

I also use it for what you call my “mud pie experiences. I shape loaves, roll gnocchi, use it to catch the pasta as it extrudes from my Kitchen Aid. It corrals small parts when I try to repair things, and contains gluey messes and beads when I make jewelry.

Do you have a favorite pan?

Hi,Gail. I admit to liking me my cooking and baking toys, but if I had to choose which one to take to the proverbial desert island, I’m pretty sure the half sheet pan would be it! Years ago I bought them for my siblings as Christmas gifts, and now none of them will use anything else! SusanHi Susan: As a professional baker for over 25 years, you appear to be confusing square inches with cubic inches. Cubic inches takes into consideration the depth of the pan also. At the bakery, we made many items in the half sheet and whole sheet pans. So long as the depth of the items is the same, a half sheet holds twice as much, not 1 1/2 times, as a 9×13 pan. If someone uses your formula for an item that is only 1/2 to 3/4 inches tall, they are going to be woefully short when they transfer it to a half sheet using the 1.5.

Just an obsversation. If you go to http://pastrieslikeapro.com/2013/09/pan-size-conversions/#.VF98FocT2EM there is an entire article on pan size conversion. Hope this helps.

Hi, Helen. I’m well aware that the calculation needed to be most accurate is for volume, not area. As I confessed early on, math has never been my first love, and the point I was trying to make with my overflow is that most of us fail to take the height of the pan’s sides into account, because most of the pans home bakers use have higher sides, until they move up to half sheet pans. Thanks so much for the link, though. I keep a file on hand of reference information, and it will fit in there very nicely! SusanI agree with Helen. If you’d started out comparing volume in this piece, it would be much less confusing for those who don’t already understand this. My favorite tip from Julia Child was to measure volume of all my baking pans and mark it on the bottom with a bold Magic Marker (Sharpie for the “young-uns”).

Thanks for the post! The problem I have when scaling up or down is the baking time. How do I figure that correctly? I would love to see bake-to temps in all your recipes.

Irene, it’s difficult to give exact times for scaling because there are so many options when changing a pan size. Your best bet is the usual way of testing items, by using your senses and a skewer. Additionally, we try to post bake-to temps for all viable items like cakes, cheesecakes and breads: bake to temps don’t work for smaller items like cookies, scones, or muffins! Laurie@KAF

What would you do for a 7in. by 11in. pan? That would be 77 sq. inches total. What is the formula for that size? Used for bar cookie or small sheet cake recipes.

Hi, Deborah. Strictly speaking, if you wanted the math to strictly line up, the conversion factor is 2.25, which I will be the first to admit is an annoying number to work with. I’m willing to bet that there’s enough headroom in the half sheet pan to try 2.5 times the bar ban’s recipe amounts. SusanI get all that, but what about eggs? I can’t half an egg. Well, I could, if I beat it first.

Hi, Suzanne. I deal with the half an egg thing in one of two ways. Most often, I keep a carton of egg beaters in the house, and simply pour out 2 tablespoons of that for the half egg if that’s what the math calls for. The other thing I do is back off the recipe’s liquid by 2 tablespoons and just go with another whole egg. SusanI always just double the recipe for a 1/2 sheet because doubling is easier than one and a halfing.

To solve the over flow problem, I just tear off a long sheet of foil, fild it into a strip about 2 inches wide and make a pan extender. It stays put because I grease the sides first. Then I lay my parchment on the bottom.

Try it. Been working a charm for me for a whole lot of years.

Cris, what you’re doing is a home version of what restaurants have in hand; stainless steel collars that fit inside the half sheet that form higher sides. I have not trouble with the 1.5, but if your homemade extender is working, no reason not to keep on with it! SusanSo why hasn’t someone made a sheet pan with 2″ high sides??

There are professional baking pans like this, Bonnie, but you don’t see them around much for home bakers. Barb@KAF

Thank You! This is something I really wanted to know.

You’re very welcome! Barb@KAF

Susan, when you bake a cake in the half-sheet pan, do you place a nail or one of those metal thingamajigs (can’t think of the name – hope you know what I’m talking about), in the center to make sure the batter in the center is fully cooked, or is it better to reduce the temp by 25 degrees, or is neither necessary? I find with cake batter especially that innermost batter isn’t always done while the edges are almost overdone. Thanks

Hi, Martibeth. I use a cake core (the aluminum tapered cup that goes in the center) when I’m doing wedding cake layers that are more than 2″ tall and more than 12″ in diameter; they help the cake cook more evenly. When it comes to half sheet pans, the layers aren’t so thick that it’s a big concern. The nice thing about doing sheet cakes is that the layers come out a nice, even 1 1/2″ tall, so when you have two layers, some filling, and frosting on top your creation is PLENTY tall enough, without having to split layers. I’ve never needed to lower the temp; I just keep an eye on the layer and the moment I see it start to pull from the edge of the pan, out it comes. Susanthank you, very helpful article! i’d love to see a similar article on round pans and loaf pans. like how many mini loaf pans equal a 1lb or 1.5 lb loaf pan. how many 6 inch pans equal 8 or 9 inch pans etc. and for cheesecake and removable bottom pans, too. thanks!

Thanks for the great suggestion, Lisa! Barb@KAF

Fill your pans with water, measure the water, do the math 🙂 Or measure side to side and depth for circular pan… pi r squared = square inches, x depth = total volume. For square/rectangle pans like your loaf pans measure as Susan says, both side ways + depth. I’ve written on pans with a Sharpie but it comes off in the washing. Better to write it in the frontispiece of your favorite cookbook.

You might also help folks convert recipes from round to square pans. Most cake recipes are for either 8 or 9 ” round. I’m hooked on the easy to slice square layer cake. Love the beautiful slices and it is easy to cut a very thin slice. Just make sure your “icing lover” guest gets the end slice!

Good idea, Meg! Barb@KAF

Thanks for the great info. I volunteer at the Twin Cities Ronald McDonald House every Monday and if I don’t bake brownies I hear about it,lol. I use three (any brand) 9X13 brownie mixes in a half sheet pan and fits perfectly. Why does that work for me?

Hi, Jill. It works because most manufacturers have steadily been shrinking the sizes of their mixes for cost-reduction purposes. It used to be you’d get much more mix in each box than you do today. Cake mixes, in particular, have been getting smaller and smaller. SusanWell, I think it depends on what you are making. I can see cake batter being a problem but I made a double batch of the Cook’s Country Blondie recipe. It’s for a 13×9 and I doubled it and baked it in a half sheet pan and it was perfect. Blondies don’t rise high like a cake. If I had done 1.5 it would have been too thin.

Different recipes are going to behave differently, of course, and since I don’t know the amounts the Cook’s Country recipe calls for, I can’t judge. Our brownie recipe for a 9 x 13 pan DEFINITELY overflows a half sheet pan if you double it, particularly if you’re putting in a healthy amount of chips or nuts. SusanThanks Susan! This post will be a big help. Now, about the “…don’t want to stare down a 9″ x 13″ pan of brownies for two weeks.” That must be an East Coast phenomena. 😉

Hi, Tom! I’ve heard people actually say a 9″ x 13″ pan makes too much. I don’t quite get it either. 🙂 SusanYou can also fill pans with water and measure the amount each holds, then perform the math to decide how much to scale the recipe up or down.

That’s right, Karen, and that’s how we measure new products to get an accurate reading on their capacity; one thing to add is that for cake batter, it’s important not to fill a pan more than 2/3 full, to allow for vertical expansion. SusanWhen I read your statement “Your favorite cake recipe calls for a 9” x 13” pan. You want to double it for a crowd, and bake it in a half-sheet (18” x 13”) pan. DON’T DO IT.” in a Facebook post, I just had to go check out the link because I’ve been doubling recipes for, uh, MANY years (not counting that high today!) and always double a 9 x 13 recipe for an 18×12 pan. Reading on I realized what what I think of as a 1/2 sheet pan is 2″ high, not that itty bitty short thing pictured. I think of your pan, which I also have, as a cookie sheet! Terminology, the downfall of precision bakers. : )

Hi, Princess. You have a 2″ high 18″ x 13″ cake pan? Cool! Life in restaurant land taught me about sheet pans firs (the big mac daddies, 18″ x 24″. From there it was half and quarter when we went smaller. I’ve seen steel collars for sheet pans to make them larger capacity, but never a cake pan that size. I’m sure they exist, but it’s probably a good thing for my home storage situation that I haven’t found one so far!! SusanYes, terminology can trip us all up at times! Barb@KAF

I am using this in my middle school math class, area, volume and ratios. Love it!

Great idea, Pat! Nice way to show your students the practical applications of math! Will you be baking with them too? Or maybe offering some cake as a reward for their mathematical labors? Barb@KAF

Never thought about it, but just to make it simple, are there not 2″ high sheet pans one can buy? LOL

They do make half sheet pans with 2″ sides, although we do not carry a pan like this. Check online. Barb@KAF

I have a half-sheet cake pan with high sides for a half sheet cake. Does that mean i can double the recipe for a 9″ X 13″ pan?

If the dimensions of your pan are 18″ X 13″ X 2″ you should be able to double a recipe written for a 9″ X 13″ pan. Barb@KAF

Invest in a half sheet pan that is two inches deep. Easy to find on line for about $20. I discovered them when I became frustrated with a Barefoot Contessa recipe for pecan pie squares which calls for baking in a half sheet pan and always overflows, making a horrible mess in the oven. But not anymore! The two inch deep half sheet pan is my absolute favorite pan— it even comes with a plastic cover that snaps on!!

Very informative, thank you. Since we are empty nesters now, are there any tricks to down sizing a recipe. Love to bake but my husband is not too keen on sweets and I do not want to be left eating it all.

Hi, Kathy. I’ve been known to take an 8″ square pan recipe, cut it in half, and bake it in an 8 1/2″ x 4″ loaf pan. It works, and it’s a pretty reasonable amount for one person over the space of a week. SusanI want to double the ginger squares and bake in a half sheet pan. I know you multiply by 1.5 but can you give a ballpark figure for baking time? I know ovens vary but, as I said, just need the Fenway estimate!

Baking time should be approximately the same, maybe a bit longer. Check at the recommended time and go from there. Barb@KAF

Thank you for the formula. I have done this conversion for years! It’s a great way to serve a crowd, everyone can have a bite.

That makes two of us, Wesly! SusanI agree with Lisa F. My big bug-a-boo is loaf and tea pans and what to do with them. I have two of KAF’s tea loaf pans, which I have never used for baking for that very reason. It’s a real shame, however they do work for meatloaf – what doesn’t?

Hi, Gloria. If you have any quickbread recipe that calls for a 9″ x 5″ pan, that’s when to reach for the tea loaf pan. It’s PERFECT for all of those recipes. Also works for a cake or pound cake recipe: any recipe where the batter around 6 cups (standard cake pan recipe). SusanThank you, thank you, thank YOU for this handy baking guide for the math challenged. There’s just part of my brain that can’t compute numbers so this is a big help!

My pleasure, Laura. Once you walk the path once or twice, it will get WAY easier! SusanDoes K.A.F. sell the half sheet pans with 2″sides?

No, Lois, we don’t; it’s quite a specialty item, usually only found in bakeries. You might try the Webstaurant store… SusanCan you write about increasing bread recipe sizes sometime? So many recipes call for the loaf to be baked in a 8 1/2 by 4 1/2 loaf pan, but I’d like to size up to a 10 x 5. I’ve struggled to figure out the math on this conversion!

Sure, good idea – I’ll add it to my list. Cheers! PJH

I found this on pinterest today and it has been really helpful. I looked through some of the comments and noticed a few people asking about half sheet cake pans with 2″ sides. I found one today at Michael’s and it is made by Wilton.

Hi there! Excellent article. Thank you. What is the formula for converting 9 x 9 to a half sheet?

Using the conversion factor of 1.5 should work in your 13 x 18 half sheet pan, Elizabeth. Happy baking! Elisabeth@KAF

how do you prevent leakage from the corners of a sheet extender, someone suggested bread?

You can line the inside edges with aluminum foil to create a barrier. Just be sure to spray it with a bit of non-stick spray to ensure an easy release. Happy baking! Kye@KAF