ACOS calculator: break-even, floor and max CPC.
Three numbers decide whether an Amazon ad can make money: what a unit leaves you before ads, what a click costs, and how often a click becomes a unit. Enter yours to see your break-even ACOS, the ACOS floor your price sets, and the most you can pay per click.
Example: price, CPC and conversion rate are from the redacted shower curtain liner audit (Amazon.com, Jul 21 – Aug 19, 2026); the unit cost is illustrative. Nothing you type leaves your browser.
How the numbers are calculated
ACOS floor = ad cost per unit ÷ price
Why the floor matters more than the bid
In the shower curtain liner account, a click cost $1.61 and 42% of clicks became a unit. That is $3.83 of advertising behind every unit, on a $10.49 average price — an ACOS of about 36.5% before anyone touches a bid (36.6% in the report, which works from unrounded figures). The best keyword in the account only got to about 33%.
Below the floor, lowering bids mostly buys fewer clicks, not cheaper units. The levers that move the floor are the unit price, the conversion rate (listing, reviews, stock, placement) and, through break-even, the unit cost. The audit found exactly that: “Don’t cut keywords. Reprice the structure.”
ACOS is one ratio. The audit reads nine.
A healthy ACOS can hide a cost per order that is wrong for the basket size, or ads carrying orders that organic rank can’t hold. That is why a Sapientia audit scores ACOS as one of nine dimensions, next to TACoS, organic rank, placements and campaign structure.
Questions
What is a good ACOS on Amazon?
One below your break-even ACOS — your profit margin before advertising. A 30% ACOS is profitable on a product with a 45% margin and loses money on one with a 25% margin, so there is no single good number.
How do I calculate break-even ACOS?
Subtract everything a unit costs you except advertising (product cost, Amazon referral and fulfilment fees, shipping) from the selling price, then divide by the selling price.
What is the ACOS floor?
The lowest ACOS your current cost per click and conversion rate allow: ad cost per unit (CPC ÷ conversion rate) divided by the price. Bids move CPC a little; if the floor is above break-even, the levers are price, conversion and unit cost.
What is the difference between ACOS and TACoS?
ACOS divides ad spend by ad-attributed sales. TACoS divides the same ad spend by total sales, organic included, so it shows whether advertising is lifting the whole business or only buying the sales it reports.
Which conversion rate should I use?
Units ordered per click from your advertising reports for the same product and period as the CPC. Mixing a top-of-search CPC with an account-wide conversion rate will give a misleading floor.
Check the other eight dimensions.
The calculator covers one ratio. A free audit scores all nine for one ASIN in about 30 minutes.
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