https://profitmetrics.io/roas-vs-poas-why-roas-is-not-the-be...

In theory, ROAS or Return On Ad Spend is a great metric. If the Return is greater than the ad spend, you’ve made money on the campaign. However, the Return (profit) is not readily available in e-commerce analytics, thereby unavailable to Google, Facebook, and other marketing channels (that’s why we’ve made ProfitMetrics). So, along the way, they decided to switch Return for the readily available, but untransparent Revenue. So most often, ROAS is short for Revenue on Ad Spend, which is an entirely different thing than Return On Ad Spend.

Revenue tells you nothing about margins, fixed costs, payment fees, and shipping costs, which are some of the most critical factors in running a profitable e-commerce business.

Let’s make one thing clear before we move on: ROAS has been considered best practice for a long time simply because it was the best metric available to most e-commerce businesses.However, as you will see below, ROAS based on Revenue comes with pitfalls that may be blocking your profitability and success.
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So we have concluded that ROAS does not allow you to fulfill your online advertising’s full potential. Let’s have a look at POAS and how POAS will enable you to do just that.

What is POAS?
POAS = Profit on Ad Spend. ROAS = Return (revenue) on Ad Spend

POAS is short for Profit on Ad Spend. It is an alternative abbreviation for the original ROAS which, as explained, was meant to be Return on Ad Spend but ended up becoming Revenue on Ad Spend.

To find the POAS of your online advertising, you divide the gross profit attributable to the online marketing channel with the ad spend. These numbers are directly comparable, meaning that a POAS higher than one (1) means you have made money.

Why POAS is the better metric
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