The three metrics, defined
ROAS (Return on Ad Spend) = Ad revenue ÷ Ad spend. A ROAS of 4 means every $1 of ad spend generated $4 of ad-attributed revenue.
ACOS (Advertising Cost of Sale) = Ad spend ÷ Ad revenue — literally the inverse of ROAS, expressed as a percentage. An ACOS of 25% is mathematically the same efficiency as a ROAS of 4.
TACOS (Total Advertising Cost of Sale) = Ad spend ÷ total revenue (ad-attributed and organic combined). This is the metric the other two leave out: it captures whether your advertising is helping total sales, including organic sales potentially lifted by ad-driven visibility, not just the sales ads get direct credit for.
Worked example
A listing generates $2,000 in ad-attributed revenue and $2,000 more in organic revenue in the same week, from $500 of ad spend.
ROAS = $2,000 ÷ $500 = 4.0. ACOS = $500 ÷ $2,000 = 25%. TACOS = $500 ÷ $4,000 (total revenue) = 12.5%.
A second worked example: watching TACOS over time
The same seller tracks TACOS over three months while keeping ad spend roughly flat: Month 1 organic revenue is $2,000 (TACOS 12.5%, as above). By Month 3, ad spend is still around $500/week, ad-attributed revenue has held steady near $2,000, but organic revenue has grown to $3,500/week as the listing's improved visibility and review count start driving more unpaid sales. TACOS falls to $500 ÷ $5,500 ≈ 9.1% — the same ad spend is now supporting a larger base of total revenue, a sign the advertising is building durable visibility rather than just buying the same fixed slice of sales every week.
Why TACOS matters even though it's harder to act on directly
ACOS and ROAS can look great on a campaign that's simply capturing sales that would have happened organically anyway (cannibalization), while TACOS trending down over time — even with steady or rising ad spend — is a genuine signal that advertising is building durable organic visibility, not just buying the same sales twice.
Where break-even ACOS fits in
Before setting a target ACOS, it's worth knowing your break-even ACOS — the ACOS at which ad-driven sales stop contributing any profit at all, calculated from your margin (see Break-Even ROAS, Explained and The Full Cost Stack of a Marketplace Sale). A campaign performing "well" relative to a category benchmark can still be losing money if your actual margin is thinner than the benchmark assumes — always check ACOS against your own break-even point, not just against a general industry range.
Which one to prioritize
Use ACOS/ROAS for day-to-day campaign optimization decisions (they respond quickly to bid and targeting changes). Track TACOS as a slower-moving, monthly-level health metric for whether your overall advertising investment is paying off across the whole listing, not just within the ad platform's own attribution.
Common mistakes with these metrics
- Comparing ACOS across products with very different margins as if a "good" ACOS is a universal number — a 30% ACOS might be very profitable on a high-margin product and a loss on a thin-margin one.
- Reacting to weekly ACOS swings on low-volume campaigns as if they're meaningful trends, when they're often just small-sample noise.
- Never tracking TACOS at all, and as a result missing the signal that a campaign generating an "acceptable" ACOS is mostly cannibalizing organic sales rather than adding incremental ones.
- Treating ROAS as if higher is always strictly better — a very high ROAS on a tiny amount of spend and a very low budget-capped impression count can mean you're leaving profitable growth on the table by under-investing, not proof the campaign is optimally sized.
Quick reference table
| Metric | Formula | Answers | Best used for |
|---|---|---|---|
| ROAS | Ad revenue ÷ Ad spend | How much revenue per ad dollar | Quick efficiency comparisons |
| ACOS | Ad spend ÷ Ad revenue | What % of ad revenue went to ads | Day-to-day campaign tuning |
| TACOS | Ad spend ÷ Total revenue | Is advertising helping total sales | Monthly/quarterly health check |
FAQs
Is a lower ACOS always better? Generally yes for efficiency, but an ACOS so low it comes with very few impressions may mean you're under-bidding relative to what your margin could actually support — see Bidding and Budgeting Strategy.
Can TACOS go up even when ACOS is stable? Yes — if organic revenue falls while ad spend and ad revenue hold steady, TACOS rises even though ACOS looks unchanged, since TACOS depends on total revenue, not just ad-attributed revenue.
What's a "good" TACOS? There's no universal benchmark — what matters is the trend for your own listing over time, ideally moving down or holding steady as organic revenue grows, rather than comparing to someone else's number in a different category with different margins.