Advertising
What is ACoS?
Advertising Cost of Sales
Ad spend divided by the revenue those ads generated. It measures how efficient a single campaign is, so a lower ACoS means each advertised sale cost you less.
Why it matters in practice
ACoS answers one narrow question well: for the sales an ad campaign got direct credit for, what did that credit cost. That is genuinely useful for comparing two campaigns against each other, and it is a poor way to judge a whole account, because it says nothing about the organic sales the same advertising helped create. A low ACoS is not automatically good either. Spend can be cut until only the safest, lowest-volume searches are left, which flatters the number while shrinking the business. The figure only becomes a decision once you know your break-even ACoS, the point where an extra advertised sale stops adding profit, because that is what turns a percentage into a ceiling you can actually bid against.
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