I use simple syrup to moisten my cakes after torting them but I was wondering if anyone has a ratio or quantity to use for say, an 8-inch cake or a 10-inch cake. For example, 1 /2 cup simple syrup to moisten an 8-inch cake so it is moist and delicious?? TIA!!

A cake shouldn't need simple syrup to be moist. It should be moist on its own based on the recipe. Flavored simple syrups are used to add an additional depth of flavor to a cake that is balanced to accept the syrup.

So to answer your question, I would look for a new recipe.

I think if you added the ssimple syrup to all the layers it will sag down ,
I have a bakery around where they add it to the bottom layer only not to all layers

Thanks scp1127 and wafawafa! I add it to both layers and haven't seen them sag.. maybe I don't add much.

scp, my recipe uses oil and a good amount of eggs but turns out dense so I add simple syrup to moisten it and make it soft. I do that just for the vanilla cake. My chocolate cake is really moist so I don't use simple syrup in that.