You can't call it a full sheet just because it's the largest size pan that you own, or the biggest one that fits in your oven. You need to follow the industry standard.
I wrote this in another thread... hope it helps:
A commercial Bun pan is 18" x 26" (outside measurement), and because they are tapered for nesting or making them stackable, the inside measurement is 16.5" x 24.5".
A commercial full sheet is 16" x 24". They are baked in 16" x 24" bakeable cardboard trays that fit into the Bun pans (flat surface portion) which are used during baking for support and handling purposes.
A true commercial full sheet (16" x 24") serves 96 (unit wt. 106-124 oz.).
If this size pan doesn't fit in your oven, and you are baking two 12" x 18" (54 serving) half sheets, they would serve 108 total.
I have a 12x18 pan and have seen that it will serve any where from 70 to 98.
A 12x18 serves 54 (single layer, cut in industry standard 2x2x2" pieces, which means the cake will be cut in 6 rows by 9 columns.)
A 2-layer 12x18 will serve 108, when cut in industry standard 1x2x4", which means the cake will be cut in 9 rows by 12 columns.
I think the full sheet and 1/2 sheet sizes vary from person to person!
No it doesn't. That's like saying "Well, it's red to me but some call it blue." Red is red; blue is blue; a full sheet is a full sheet. The only reason it "varies from person to person" is if a person doesn't have the correct information.
One can't "just decide" what size it is.
CWR, great history on cake sizes! 
I have a 12x18 pan and have seen that it will serve any where from 70 to 98.
A 12x18 serves 54 (single layer, cut in industry standard 2x2x2" pieces, which means the cake will be cut in 6 rows by 9 columns.)
A 2-layer 12x18 will serve 108, when cut in industry standard 1x2x4", which means the cake will be cut in 9 rows by 12 columns.
I think the full sheet and 1/2 sheet sizes vary from person to person!
No it doesn't. That's like saying "Well, it's red to me but some call it blue." Red is red; blue is blue; a full sheet is a full sheet. The only reason it "varies from person to person" is if a person doesn't have the correct information.
One can't "just decide" what size it is.
CWR, great history on cake sizes!
And I did not say it was for sure the full sheet size or not, so its not red because i said it was red or blue because you said it was blue....sorry for my input!
sorry to steal the thread 
but since y'all are giving TRUE sizes here (googled it, and came up with everything from 'if it fits in your oven' to '16X24' to '4 9X8's laid in a square pattern' and 'anything that will feed 105 people'... so I want the TRUTH and we all know you cant always belive what you read, unless its on CC and verified )
what is a half and a quarter? Please?? I'm thinking I make mine way too big and want to make sure I'm doing it right
I work at a bakery. Our half sheets are 12x16 because we bake 2 at at time using pan "extenders". The Magic Line half sheet pan I bought at a party sttore is a 12x18. Same for a quarter sheet..we bake 4 at a time using "extenders" and they "measure" at a 8x12. But if you buy a magic line quarter sheet pan, it is a 9x12. But I would never call a 12x18 a "full sheet". It is known in the industry as a half sheet. Again, there are many fluctuations/opinions to determine a half, quarter or full sheet on line. Guess I just gave mine! 
And I did not say it was for sure the full sheet size or not...
I forgot to add my disclaimer too...
"I'm not saying 'for sure' the measurement I gave is for a full sheet size or not." (and I don't use the 12X18 for my full sheet especially if/when people expect "full" to serve approximately 100, but receive only half that size)!
18"x24" = full sheet
cut that in half and you get two 12"x18" half sheet cakes
cut each of those in half and you get four 9"x12" quarter sheet cakes
I know not everyone follows this standard, but that doesn't change the fact that this IS the standard and that anyone NOT following it is deviating (therefore, wrong).
And I did not say it was for sure the full sheet size or not...
I forgot to add my disclaimer too...
"I'm not saying 'for sure' the measurement I gave is for a full sheet size or not." (and I don't use the 12X18 for my full sheet especially if/when people expect "full" to serve approximately 100, but receive only half that size)!
When customers ask me for a full sheet, they get told exactly what MY sizes are and how many MY cakes will feed....not what other people make or tell me.....ahhhhh
18"x24" = full sheet
cut that in half and you get two 12"x18" half sheet cakes
cut each of those in half and you get four 9"x12" quarter sheet cakes
I know not everyone follows this standard, but that doesn't change the fact that this IS the standard and that anyone NOT following it is deviating (therefore, wrong).
Sure... and Wilton that help to set the standard probably 75-80 years ago must be wrong too. That's why they list standard quarter sheet pan/serving sizes as 9x13. Too bad all those pan manufacturers aren't making the correct size (when was the last time anyone found a 9x12 pan to purchase anyway?) If you worked at a wholesale commercial baking factory, or ordered prebaked frozen cases of full sheet cakes, you'd know they aren't all doing it wrong. Just call any major baking manufacturer or distributor and ask for the size and unit weight, or view it in their catalog... it's nothing new, they've been doing it the same way for many, many years (and they haven't thrown away all of their pans to match someone elses standard).
18"x24" = full sheet
cut that in half and you get two 12"x18" half sheet cakes
cut each of those in half and you get four 9"x12" quarter sheet cakes
I know not everyone follows this standard, but that doesn't change the fact that this IS the standard and that anyone NOT following it is deviating (therefore, wrong).
Sure... and Wilton that help to set the standard probably 75-80 years ago must be wrong too. That's why they list standard quarter sheet pan/serving sizes as 9x13. Too bad all those pan manufacturers aren't making the correct size (when was the last time anyone found a 9x12 pan to purchase anyway?) If you worked at a wholesale commercial baking factory, or ordered prebaked frozen cases of full sheet cakes, you'd know they aren't all doing it wrong. Just call any major baking manufacturer or distributor and ask for the size and unit weight, or view it in their catalog... it's nothing new, they've been doing it the same way for many, many years (and they haven't thrown away all of their pans to match someone elses standard).
Commercial bakeries don't waste time baking individual 9x13 cakes. They bake full sheets and cut them down into halves and quarters, which yields the sizes I stated above. I have no idea why the 9x12 was upped to a 9x13 for the individual quarter sheet pan. Wilton is geared towards the home baker. I wouldn't exactly rely on them for commercial bakery standards.
I have no idea why the 9x12 was upped to a 9x13 for the individual quarter sheet pan.
I'm just taking a shot in the dark here, but I remember my 9x13 pan from forever ago and I recall that it was flaired. If someone has a 9x13, could they pull it out and check a measurement? I'm thinking the top of the pan would be 9x13 but the bottom of the pan may end up being more of 9x12?
Just a theory based on my recollections of home-use pans having the flaired sides.
Commercial bakeries don't waste time baking individual 9x13 cakes. They bake full sheets and cut them down into halves and quarters, which yields the sizes I stated above. I have no idea why the 9x12 was upped to a 9x13 for the individual quarter sheet pan. Wilton is geared towards the home baker. I wouldn't exactly rely on them for commercial bakery standards.
Funny... I worked in a commercial bakery that distributed worldwide, and we NEVER cut down ANYTHING. Can you imagine the complaints/returns or non-potential orders if customers were to receive cakes that were cut down or trimmed to another size? Nobody wants to deal with raw edges and crumbs--yuck! They got exactly what they ordered, not something that looked like the order was made incorrectly and "fixed" to represent something else. The commercial full sheets are never 18x24 to begin with, so if they were cut in half they would never equal 12x18 anyway. The 12x18 cakes aren't baked individually, there are two 1/2 sheet pans welded together with a space in between, so they get handled the same way as the full sheet trays.
You can't call it a full sheet just because it's the largest size pan that you own, or the biggest one that fits in your oven. You need to follow the industry standard.
I wrote this in another thread... hope it helps:
A commercial Bun pan is 18" x 26" (outside measurement), and because they are tapered for nesting or making them stackable, the inside measurement is 16.5" x 24.5".
A commercial full sheet is 16" x 24". They are baked in 16" x 24" bakeable cardboard trays that fit into the Bun pans (flat surface portion) which are used during baking for support and handling purposes.
A true commercial full sheet (16" x 24") serves 96 (unit wt. 106-124 oz.).
If this size pan doesn't fit in your oven, and you are baking two 12" x 18" (54 serving) half sheets, they would serve 108 total.
Wonderful info thanks for taking the time to post this!
Slightly off subject but I wanted to share. When is a dozen not 12? I had a customer call about cupcakes and asked the price for a dozen. I told her and then she asked me about many cupcakes were in a dozen. It turns out that she had order a dozen cupcakes from someone before and had only gotten 6. She asked them why she only had 6 and they said that was their dozen. The only thing I could think is that she got jumbo cupcakes instead of normal, but still, she wanted a dozen.
Slightly off subject but I wanted to share. When is a dozen not 12? I had a customer call about cupcakes and asked the price for a dozen. I told her and then she asked me about many cupcakes were in a dozen. It turns out that she had order a dozen cupcakes from someone before and had only gotten 6. She asked them why she only had 6 and they said that was their dozen. The only thing I could think is that she got jumbo cupcakes instead of normal, but still, she wanted a dozen.
wow...I have never heard anything like that...ugh!
for me a dozen is 12...always will be.
Commercial bakeries don't waste time baking individual 9x13 cakes. They bake full sheets and cut them down into halves and quarters, which yields the sizes I stated above. I have no idea why the 9x12 was upped to a 9x13 for the individual quarter sheet pan. Wilton is geared towards the home baker. I wouldn't exactly rely on them for commercial bakery standards.
Funny... I worked in a commercial bakery that distributed worldwide, and we NEVER cut down ANYTHING. Can you imagine the complaints/returns or non-potential orders if customers were to receive cakes that were cut down or trimmed to another size? Nobody wants to deal with raw edges and crumbs--yuck! They got exactly what they ordered, not something that looked like the order was made incorrectly and "fixed" to represent something else. The commercial full sheets are never 18x24 to begin with, so if they were cut in half they would never equal 12x18 anyway. The 12x18 cakes aren't baked individually, there are two 1/2 sheet pans welded together with a space in between, so they get handled the same way as the full sheet trays.
Whenever you carve a cake into a shape you have raw edges. I, too, have worked in a commercial bakery and we always cut cakes down. Full sheets to half sheets to quarter sheets. I have no idea why you think this makes it look like cakes aren't made to order. After all, you're going to have many more than one order for any give flavor. Why bake 4 quarter sheets when you could bake 1 full sheet and cut into four cakes? That's one pan to clean vs 4. Just because the bakery you worked at did things one way, doesn't mean that that's the way most bakeries do things. (I know you're wanting to counter me with the same statement, but from the research I've done, what I've stated is the norm and what you described is the exception).
Whenever you carve a cake into a shape you have raw edges. I, too, have worked in a commercial bakery and we always cut cakes down. Full sheets to half sheets to quarter sheets. I have no idea why you think this makes it look like cakes aren't made to order. After all, you're going to have many more than one order for any give flavor. Why bake 4 quarter sheets when you could bake 1 full sheet and cut into four cakes? That's one pan to clean vs 4. Just because the bakery you worked at did things one way, doesn't mean that that's the way most bakeries do things. (I know you're wanting to counter me with the same statement, but from the research I've done, what I've stated is the norm and what you described is the exception).
Thats your opinion, and you know what they say about opinions...
You can do all the research you wantIm not talking about most bakeries, Im talking about WHOLESALE Commercial Bakeries. Wholesale commercial bakeries dont carve a cake into a shape with raw edges in the first placethats the work of custom cake shops.
Of course commercial means more than one order per flavor. Ours were packed 3 per case, 36 per pallet, with a 100 pallet minimum order (for a total of 10,800 full sheet cakes). AND, you only got the best price if you were ordering over 1400 cases at a time. If you wanted to order fewer cases than the 100 pallet minimum, you had to go through a brokerage house. Thats what a wholesale commercial bakery is... unbelievable volume, thousands of employees, and non-stop production day and night during three full shifts.
As I mentioned earlier, everything is handled just like full sheetsfour quarter sheets per pan, two half sheets per pan, six 6, 7, & 8 per pan, and these pans are welded together. Everything fits within the brackets of pan racks. Why would a production facility make any extra step to cut anything when they can bake the appropriate size and not waste any time doing anything else to it? They are baking four quarter sheets in the same amount of oven space as one full sheet and they dont have four pans to clean, its one. Furthermore, nobody cares how many pans needed cleaning when its all automated!
If the commercial bakery you worked at used the standard 16 x 24 bakeable cardboard tray to line the full sheet pans and you removed them all from the trays to cut, what did they place them in for shipping? You know the sides arent tall enough to bake standard height cakes without the bakeable trays unless youre baking short sponge cakes on top of parchment to use for log rolls.
How many baking manufacturers or distributors have you called for your research? Id be happy to hook you up with some names of wholesale manufacturers if youd like to further your research on actual standard sizes.
I think your sweeping generalization by stating that anyone NOT following (your interpretation of) standard is deviating and therefore wrong is a bit too strong. (Oh wait... I see your motto in your signatureApparently, anyone who disagrees with you is already wrong!) Thats not very friendly, kind, compassionate, or open-minded. Wow! I dont normally care to help others that have that attitude, so forgive me if my experience or willingness to share knowledge has offended you. (My offer still stands if youd like to be enlightened.)
CWR41: I think I know you! I believe we worked at the same place. If so, that place is HUGE. I mean seriously, our building along must have been something like 3 million sq. ft. And those ovens, I'd guess probably 9,000 sq. ft.???
I still have at least one of their old catalogs with all the info, and a few from the other wholesalers too. (I guess I can't scan them to post because they aren't decorated cake photos.)
I agree, I don't like sharing info for free with those who don't appreciate it. Please send me a PM or better yet, call me if you think you know who I am (I've had the same phone number for nearly 27 years!)
P.S. If there's anyone else out there who thinks we may have worked together at this giant plant, please respond or PM me. I'll give you a hint who I am... "Follow Me!" (if that means anything to you). Maybe we can plan a get-together!
Im talking about WHOLESALE Commercial Bakeries.
Yeah, because wholesale really compares to the world of couture cakes... 
I really don't understand why you're using a wholesale bakery's practices as a reference here. I don't think anyone who posts here is looking to start-up a wholesale bakery. Nor was anyone asking about the wholesale industry's practices and standards.
Obviously, I don't really know anything about wholesale bakeries, but then I have no desire, to, either. It's just so far from what I do and what most people on this website do. Would you use a blanket factory's practices as a reference in a discussion with people who quilt by hand? 
I think your sweeping generalization by stating that anyone NOT following (your interpretation of) standard is deviating and therefore wrong is a bit too strong. (Oh wait... I see your motto in your signatureApparently, anyone who disagrees with you is already wrong!) Thats not very friendly, kind, compassionate, or open-minded. Wow! I dont normally care to help others that have that attitude, so forgive me if my experience or willingness to share knowledge has offended you. (My offer still stands if youd like to be enlightened.)
Um, I'm not the only one who quotes this industry standard. It's not MY interpretation of it. It's just the way it is. But, then, again, I'm not talking about the wholesale bakery industry. Which, as I stated above, really just doesn't pertain to this discussion.
As for my sig line. Um, did you not notice the 
at the end? It's a joke. But I guess you're too busy getting upset because I'm talking about circles and you're talking about squares to notice that.
What I really don't get is why you're taking such offense at a statement of facts and taking it as a personal attack? Just because the way the factory you worked at functions differently from couture bakers isn't a reason to get into such a high dudgeon.
Okay, the OP asked what a true full sheet cake size is (not a couture custom size) and if 12x18 is considered a full sheet. The answer to part two is no. (I guess you can decide for yourself the answer to part one based on actual pan sizes.)
Im certain that good old-fashioned bakeries, whether you want to call them commercial or wholesale, have used the same standard long before all of the custom design studios started popping up.
My post responds to the topic of sheet cake sizes, which pertains to what all of us do in one form or another (and appropriate for this website). Im talking apples (cakes), period. Im not comparing apples to oranges, nor blankets to quilts (poor analogy).
prterrell: Evidently, you quote (or repeat what youve heard as) industry standard differently from time to time, as this is what you used to say on another forum:
Quarter sheet 13-inches x 9-inches 20
Half sheet 12-inches x 18-inches 40
3/4 sheet 18-inches x 18-inches 60
Full sheet 18-inches x 30-inches 80
(I wonder how your full sheet pan grew to 18 x 30.)
and now you say:
Full = 18 x 24
Half = 12 x 18
Quarter = 9 x 12
(you can do the math based on shoving two half sheets together or cutting a half sheet in half.)
Ill stick to the answer that I know.
Jokes are suppose to be funny, not rude. Adding a smiley face to the end of You could disagree with me, but, then youd be wrong doesnt amuse me at all. (Thanks for removing it. It improves the appearance of your character greatly, and Id like to think others would agree.)
Im not upset in the leastwere all here to talk about cake! Im not taking offense either... Im just here to help answer a question, although it is beginning to feel like a personal attack on me. Peace.
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