Cost of sales, or COS, shouldn’t be confused with Content Optimization System (also the acronym COS).
Cost of sales used to be more popular than ROAS but is now rarely seen and primarily used in retail companies.
The calculation, however, is the direct opposite of ROAS. You’ll have to divide the cost with the campaign’s revenue to get the COS.
Example: Your local store for outdoor wear has been running a campaign with an ad spend of 100$. That campaign generated revenue of 410$.
100 / 410 = 0,24
The COS of that campaign is 24%.