ACoS (Advertising Cost of Sale)
Definition
Amazon's measure of ad efficiency: ad spend as a percentage of the sales those ads produced. It is the inverse of ROAS.
Want a deeper explanation?
Formula
ACoS % = Ad Spend ÷ Ad-Attributed Sales × 100ACoS only tells you something when compared with your margin. If your contribution margin before ads is 35%, a 30% ACoS is profitable; a 40% ACoS is not.
That comparison gives your break-even ACoS. Watch for: ACoS targets copied from other sellers, because the right number depends entirely on your own margins.
Example
$3,000 of ad spend that drives $10,000 of attributed sales is a 30% ACoS, which equals a 3.33 ROAS.