I use 9x13 for 1/4 sheet, 11x15 for 1/2 sheet and 12x18 for full sheet.. It really just depends on what YOU want to use for your size sheet cakes..
Hi and welcome to CC 
The thing with sheet pan sizes (as I'm sure most people on here will tell you) is that the sheet sizes are not uniform and everybody uses their own version of 1/4 or 1/2 sheet pans. I think most people consider 1/4 sheet 9x13" and 1/2 sheet 12x18". Although some people consider 1/2 sheet 11x15". Hope this helps.
I know it can be confusing. I have worked in a commerical bakery and a full sheet cake is technically 22 x 30 (I don't believe this pan will fit in a normal oven). A 1/2 sheet is usually 12 x 18 (some use 11 x 15) and a 1/4 sheet is 9 x 13.
People do seem to use different sizes, but I'd make sure that whatever youuse, that your 1/4 sheet actually is 1/4 of your full sheet, and that your 1/2 sheet really is 1/2 of your full sheet. *like if you use a 9x13 for a 1/4 sheet, then 2 of those are a 1/2 sheet and 4 of those is a full sheet
I use the following:
9x13 for 1/4 sheet
12x18 for half sheet
2--11x15 for full sheet
Really depends on your own terms.
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