I have a two tiered cake coming up and I am trying to figure out how many batches of WASC I will need.  I need enough batter to fill two 8x3 square pans and two 6x3 square pans.  

I never used 3” pans so not exactly sure   Don’t know how much difference there is between them and 2”ers as far as how much batter is needed   My guess is that it will not be much more so I’m thinking just 2 is all   To be safe what you can do is use 2 mixes with the rest of the recipe ingredients as if only one box was used OR just make 3 batches & make cupcakes with any extra batter   Sorry I can’t be more accurate 

A double batch is where I was leaning to as well.  I know for my two 6x3 pans I can fill those and still get a 6x2 layer with one batch.

But funny enough I got another order for a 12 inch round cake (one layer chocolate and one layer vanilla) right after I posted this.  So I am going to have to amp up the amount of chocolate batter I am going to have to make anyways.  So I am thinking 1 batch for the 12 inch and 2 batches for the tiered cake.  I think I should start a diary to keep track of how much batter vs cake pans now that I am getting more and more orders.

Yes, a one batter is perfect for 12x2 round.  Yes! Indeed do keep a record of how much is needed in each pan you use most.  It's soooo helpful :)  On my original post of the recipe I do give some pan combinations but of course not ALL that someone could  possibly need - as shown by the use of 3" pans - which I have never even thought of using :)

if you check the wilton wedding cake data chart -- it lists how much batter is needed in cups for each size pan -- a one box mix wasc makes about 7 cups of batter give or take -- so if you take that information you can determine how many batches you need -- for example one layer of a 6, an 8 and a 12  needs 14 cups of batter -- for two layers each, 28 cups of batter -- 4 batches or more -- if I understand what you are making --

not that anyone measures by  the individual cup full -- you can just use that info to make a better educated guess

it also has a lot of very solid info on there you can bank on --

https://www.wilton.com/cake-serving-guide/cms-baking-serving-guide.html

So after reviewing the link K8 provided as well as the other chart wilton has (https://www.wilton.com/wedding-cake-guide/cms-wedding-cake-data.html) I think I have determined that I will need 5 batches of chocolate cake.  

I did look at Fat Daddios site to see what they suggest in regards to filling their 3" deep pans and it is crazy the difference between what they say for a 12x3 and what Wilton says for a 12x3.  FD says that that size pan needs 20 cups of batter while Wilton says 11 cups.  Almost double!  But then again they also differ on how much you should fill up the pan...FD says 2/3 while Wilton says 1/2.  I was always under the assumption that you fill them 1/2 way.  Got to love the variations!

is  fd giving the total needed for both layers? wilton is giving the amount for one layer — so that could be closer than it seems maybe  —

i’m with wilton on the three inch only getting filled half full — cause i can’t get a 2/3 full three inch deep pan to bake right — although I can get the 2/3 full two inch deep pan to bake correctly — my mistakes made me a believer — but that distinction goes against the grain — a bigger pan should be able to bake off more batter — yeah but nope — not at my house anyhow —

i should go peruse fd’s chart but i’m on my phone right now...

From what I can tell, FD is talking about how much batter is needed to fill one pan 2/3 full.  And I agree with you, I have had success filling a 3" deep pan 1/2 full but more than that then I run into trouble (only ever used a 6x3 round in the past).  So even though I am using FD pans, I am going to go with Wilton on how much batter is needed.

I like using 3" deep pans because then I know I will get a solid 2" layer which I then torte into 2 - 1" layers.  Whenever I use a 2" deep pan I just can't get the dang cake to bake high enough to get a solid 2" layer without problems of overflowing.  They are always short by about a half inch after I level them.  Frustrating!

that’s exactly why I use three inchers too— to get that depth —

that fat daddyios chart -- idk -- is just seems whack-o to me -- the serving size is 1x2 -- either they need to change the number of servings or add the other dimension to the serving size --

for round 12" pans

two inches deep  = PRD-122 12"x2" cups of batter 7 7/8 cups, servings 56  

three inches deep = PRD-122 12"x3" cups of batter 15 3/4 cups, servings 56  

a 16" round takes 16 cups on wilton's and it's worked for me for ever

fd chart is screwy -- these are the squares:

PSQ-12122 12"x12"x2" 10 cups,    72servings        PSQ-12123 12"x12"x3" 20cups,    72 servings  

while it's true the footprint of the cake determines the servings -- it's not gonna actually be the same sized serving -- obviously the one with twice as much batter will be twice as big a serving -- their chart isn't efficient -- it doesn't give equal size servings and that is whack-o