If the recipe is for, say 2 9" rounds, and you need to make 2 11" rounds, or 2 6" rounds, how do you adjust your recipe? Do you just figure how many cups you will need and double or halve the recipe to get what you need?

The wilton baking chart is a good estimate for the number of cups of batter you need per pan size.

http://www.wilton.com/cakes/making-cakes/baking-party-cake-2-inch-pans.cfm

These are for 2 inch pans. I've started tracking how many of each pan size I get out of a recipe and I also weigh my pans once filled and use that instead of the number of cups. I find the weight is just faster and easier to use when making cakes.

Also some recipes rise more than others and some pans may vary. For example professional pans are a full 2 inches tall where a pan you may buy at a grocery store are usually a bit shorter..closer to 1 1/2 inches tall. All that comes into play. Hope that helps a little.

It depends on the recipe you're using, how deep your pans are etc, some of this just comes with experience and familiarity with how much your recipes yield etc. I have poured water (using a measuring cup) into my pans to figure out how many cups of batter I need and knowing my favorite recipe makes right at 5 cups of batter then I can determine whether to double the recipe, 1/2 the recipe etc.

Heres also a tutorial that might help:
http://cakecentral.com/tutorial/cake-baking-cutting-serving-guide-2-in-deep-pans

I don't bother turning on my mixer unless it's completely full to capacity. Just make whatever a full batch is for you, and bake extra layers with leftover batter to freeze for future use.

Thank you so much for your replies - and that link is great! I just printed it off.

In scratch baking, I agree with the first few answers. Every recipe responds differently and some need tweaking at different sizes. Knowing the capacity of the pans through the charts, and knowing the capacity of your recipe is important. My recipes look like science lab reports. Start making notes about cups per recipe, the amount of the rise, and anything temperamental about your recipe. You may not want to just fill your pan, as the final capacity depends on rise more than cups of batter or filling the pan. You also want the end product to produce two torted layers. And if you don't have multiple pans, that info is needed to duplicate your first baked layers for consistency.

So again, my advice is to start taking notes. I even jot down the rise on my cupcakes and what specific scoop I need to achieve the correct rise in the finished product... 1/4 from top, 1/2, or only 2/3 full. It only takes a minute and that information is so valuable when an order comes in without the time to experiment.

If you weigh your ingredients, even splitting an egg becomes simple. Less waste, more $$ for you.

For anyone starting to weigh, grams are the way to go. I'm in the process of converting my recipes from ounces to grams for the very purpose of different size cakes. I'm offering a whole line of gourmet six inch cakes and I can't be wasting ingredients.

Good suggestion to take notes scp1127. This isn't a business for me, but I still want to excel at it. I have notebooks for my soapmaking, so why not baking. Makes good sense. I'm kicking myself for not making notes on recipes I've already tried - frostings as well. Would've saved me a lot of time!