Amazon ACoS (Advertising Cost of Sale) is a metric that shows how much money you spent on advertising versus sales you received for a given product on Amazon. The formula for ACoS is 100 ( [total ad spend] ÷ [total sales] )
As a rule of a thumb, there are several ways to determine what is your Maximum ACoS for a keyword:
Profit margin
Seller's intent
Maximum ACoS
35%
10% profit
25%
35%
break-even
35%