What does ACoS stand for? Advertising Cost of Sales. It is the core efficiency metric in Amazon advertising: the share of ad-attributed sales you spent on ads to get them. Amazon writes it ACOS and defines the formula as ad spend divided by ad revenue, multiplied by 100. Spend $20 to generate $100 in ad sales, and your ACoS is 20%.
Lower is cheaper. Lower is not automatically better. Whether a given figure is healthy depends on your margin and on what the campaign is meant to achieve, and honestly, that is the part most explanations skip. This guide covers the meaning, the calculation, how ACoS relates to ROAS, and how to work out a good ACoS for your own products.
ACoS meaning, in plain terms
ACoS answers one question: for every dollar of sales my ads produced, how many cents did the ads cost? An ACoS of 25% means 25 cents of ad spend per dollar of attributed sales.
Two details matter more than they look.
It counts ad-attributed revenue only. Purchases made without anyone clicking your ad never enter the denominator. That’s why I’d never judge advertising on this ratio alone: it can make paid traffic look worse, or better, than it truly is for the business.
It is a cost ratio, not a profit measure. Twenty percent can be wonderfully profitable on a product earning a 50% margin, yet a steady loss on one earning 15%. In my view the figure means nothing until you hold it against your margin.
How to calculate ACoS
ACoS = ad spend ÷ ad-attributed sales × 100
Amazon’s own example: spend $50 on a campaign that earns $100, and your ACoS is 50%.
A second illustration, with round numbers chosen for clarity:
| Campaign A | Campaign B | |
|---|---|---|
| Ad spend | $300 | $300 |
| Ad-attributed sales | $1,500 | $750 |
| ACoS | 20% | 40% |
| ROAS | 5.0 | 2.5 |
Identical budgets, wildly different efficiency. Campaign Manager works the figure out automatically at campaign, ad group and keyword level. I’d look at keyword level first, because a healthy campaign average often hides two or three search terms burning money.
ACoS vs ROAS
ROAS (return on ad spend) is the inverse of ACoS. Amazon describes it as ad revenue divided by ad spend.
- ACoS 25% means ROAS 4.0
- ACoS 50% means ROAS 2.0
- ACoS 10% means ROAS 10.0
To convert, divide 100 by the percentage. Both describe one relationship from opposite ends, so my advice is to choose one for reporting and stick with it. Switching between them mid-conversation causes more confusion than any formula. Our guide to TACoS vs ACoS vs ROAS explains when each one is the right lens, including TACoS, which compares ad spend with total sales rather than ad sales alone.
What is a good ACoS?
Amazon’s own answer is honest: there isn’t a definitive number for a good ACOS, because it depends on your industry, size and goals. What Amazon does state is the principle that decides it: to stay profitable, your ACoS needs to be lower than your profit margin. That threshold is your break-even ACoS.
Step 1: find your break-even ACoS
Break-even ACoS is your profit margin before advertising: what is left of the selling price after product cost, Amazon fees, shipping and other per-unit costs.
An illustration with round numbers:
- Selling price: $30.00
- Product, fees, inbound shipping and other unit costs: $21.00
- Profit before advertising: $9.00
- Break-even ACoS: $9 ÷ $30 = 30%
At 30% ACoS, each ad-driven sale earns nothing, which I think every seller should know by heart for their top products. Below 30%, ad sales are profitable. Above it, each one loses money. Our guide to calculating Amazon FBA profit margin shows how to get the cost side right.
Step 2: set a target ACoS for the campaign’s job
This is where I think most sellers go wrong: they apply one target to every campaign. Better to set it by goal.
- Launching a product? You may run above break-even on purpose to buy early sales, reviews and rank. Fine, in my view, as a decision with a budget and an end date written down.
- Defending rank on a proven product? Somewhere near break-even can make sense, because the ads protect organic sales you would otherwise lose.
- Running for profit? Aim comfortably below break-even, leaving headroom for costs the ratio never sees, like returns and storage.
- Branded search terms (your own brand name) usually run at a much lower ACoS than generic terms. Judge them separately, or they flatter the average.
A low ACoS is not always good news. If ACoS is far below break-even and sales are flat, you may be under-investing and leaving profitable volume to competitors. I’d treat a very low ACoS as a question, not a trophy.
Why your ACoS can mislead you
- It ignores the organic lift. Paid clicks can push organic rank and unpaid purchases upward, and this ratio never gives them credit. TACoS captures that better, I’d argue.
- Attribution has a window. Sales are credited to ads that were clicked within a set period, so recent days look worse before late conversions arrive. Judge over a few weeks, not a day.
- Averages hide the bleeders. One campaign at 22% can contain keywords at 8% and others at 90%.
- Price changes move it. A coupon trims revenue per order and pushes the percentage up, even when the ads themselves perform identically.
A quick ACoS health check
Five questions I’d ask of any account before touching a single bid:
- Do you know your break-even per product? If not, every judgment below is guesswork.
- Which search terms spent most last month without a sale? Those are tomorrow’s negatives.
- Is branded traffic separated from generic? Mixed together, the average lies.
- Has the listing changed recently? A new main image or price can swing conversion overnight.
- Is total sales growth keeping pace with ad spend? If spend climbs while total revenue stalls, something structural is wrong.
None of these needs software. A spreadsheet and an honest hour will do.
How to lower ACoS without killing sales
- Add negative keywords for search terms that spend without converting. Our guide to optimizing negative keywords on Amazon covers the routine.
- Harvest converting search terms from auto and broad campaigns into exact match, where you control the bid. Our guide to choosing the best keywords for Amazon advertising covers the full process.
- Cut bids on keywords above break-even rather than pausing them outright, unless they never convert. I’d rather trim than kill.
- Fix the listing before raising budgets, which I’d always do first. A better main image, price or reviews lifts conversion, and higher conversion lowers ACoS on every keyword at once.
- Structure campaigns so you can see what is happening. Our guide to Amazon PPC campaign structure shows the shape.
If you would rather have this run for you, that is our Amazon advertising management service. One result published on that page: a four-brand client that came to us at ACoS above 150% and ROAS below 1.0 now runs at ACoS below 10% with a 9.0 ROAS, after three years of continuous optimization. We are an Amazon Ads partner.
FAQ
What does ACoS stand for?
ACoS stands for Advertising Cost of Sales. It is the percentage of ad-attributed sales spent on advertising to generate them, calculated as ad spend divided by ad sales, multiplied by 100. Amazon writes it as ACOS.
How do you calculate ACoS on Amazon?
Divide your ad spend by the sales attributed to those ads, then multiply by 100. Spending $50 to generate $200 in ad sales gives an ACoS of 25%. Amazon’s Campaign Manager shows ACoS for campaigns, ad groups and keywords automatically.
What is a good ACoS on Amazon?
There is no universal number. A good ACoS sits below your break-even ACoS, which equals your profit margin before advertising, with a target set by the campaign’s goal: higher during a deliberate launch, lower for profit-focused campaigns.
What is break-even ACoS?
Break-even ACoS is the ACoS at which advertising earns zero profit, and it equals your profit margin before ad costs. If a $30 product leaves $9 after all costs except advertising, break-even ACoS is 30%.
What is the difference between ACoS and ROAS?
They measure the same relationship in opposite directions. ACoS is ad spend divided by ad sales; ROAS is ad sales divided by ad spend. An ACoS of 25% equals a ROAS of 4.0.
Why is my ACoS so high?
Common causes are search terms that spend without converting, bids above what your margin supports, a weak listing that converts poorly, recent price cuts, and judging too few days of data. Negative keywords and listing fixes usually move it fastest.
Last updated: October 3, 2026. Definitions follow Amazon Ads’ published guidance; worked examples use illustrative round numbers. Sources: Amazon Ads: what is ACOS, Amazon Ads: what is ROAS.
