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Join early accessACoS
Advertising cost of salesAmazon ad spend as a percentage of the revenue those ads produced.
ACoS (advertising cost of sales) is Amazon ad spend divided by ad-attributed revenue, as a percentage. A 25% ACoS means you spent $0.25 in ads for every $1 of ad-driven sales. It's the standard measure of Amazon campaign efficiency — the inverse of ROAS.
In practice
ACoS is the number Amazon sellers manage day to day, and its main trap is that it's easy to improve by doing something harmful. Cut bids hard and ACoS falls beautifully while total sales and organic rank quietly slide. Efficiency improved; the business shrank. That's why TACoS belongs beside it — one watches the campaign, the other watches the product.
Break-even is what makes ACoS actionable. Your break-even ACoS is your contribution margin: if 35% of each sale survives product cost, Amazon fees and shipping, then a 35% ACoS breaks even exactly and anything below it is profit. Products with different margins therefore carry different targets, which is why a single blanket ACoS goal across a catalogue usually does more harm than good.
Formula
ACoS = Ad spend ÷ Ad revenue × 100
Example: $3,000 spend on $12,000 ad revenue = 25% ACoS.
What a good result depends on
A ‘good’ ACoS is at or below your break-even ACoS (set by your margin); launches run higher on purpose.
Common mistakes
- Chasing a low ACoS at the expense of total sales — that's what TACoS catches.
- Comparing ACoS across products with different margins.
Questions people ask
- What's a good ACoS?
- Anything comfortably below your break-even ACoS, which equals your contribution margin. A 20% ACoS is excellent on a 40%-margin product and loss-making on a 15%-margin one.
- Why is ACoS so high on a new product?
- Launches usually run above break-even deliberately — you're buying reviews, rank and sales velocity rather than immediate profit. The question isn't whether it's high, it's whether it's trending down as organic sales pick up.
- Is ACoS just ROAS upside down?
- Essentially, yes: ACoS = 1 ÷ ROAS × 100. A 25% ACoS and a 4× ROAS describe identical performance. The convention differs by platform, not by meaning.