ROAS and POAS both describe how well ad spend is performing — but they answer different questions, and confusing the two is one of the most common ways Shopify merchants misjudge which campaigns are actually working. If you're new to POAS specifically, our ROAS vs POAS: the metric killing your Shopify profits covers why this distinction matters in more depth.
ROAS vs POAS at a glance
| ROAS | POAS | |
|---|---|---|
| Formula | Revenue ÷ Ad Spend | (Revenue − COGS) ÷ Ad Spend |
| Measures | Revenue generated per ad dollar | Profit generated per ad dollar |
| Needs COGS data? | No | Yes |
| Break-even point | 1 ÷ gross margin (varies by product) | 1.0, always |
| When it misleads | Margin-variable catalogs — a high ROAS can hide a loss | Rarely, if COGS data is accurate |
| Native to Google Ads? | Yes, tracked by default | No — has to be built manually or with a connected tool |
The core difference in one line: ROAS tells you how much revenue a dollar of ad spend produced; POAS tells you how much of that revenue was actually yours to keep.
Worked example
Two campaigns, same spend, same revenue, same ROAS:
| Campaign | Spend | Revenue | ROAS | Margin | POAS |
|---|---|---|---|---|---|
| M | $1,000 | $4,000 | 4.0x | 20% | 0.8 |
| N | $1,000 | $4,000 | 4.0x | 50% | 2.0 |
By ROAS, these two campaigns are indistinguishable — both 4x, both look like solid performers. POAS shows the real picture: Campaign M is losing money (0.8, below the 1.0 break-even line), Campaign N is comfortably profitable (2.0). This example is walked through in more detail, including the formula for each metric, in what is POAS.
Extend it one step further: if you scaled both campaigns 50% based on ROAS alone — since they look equally strong — you'd be scaling Campaign M's loss right alongside Campaign N's profit. POAS is what tells you to scale N and fix or cut M.
Why ROAS is the default, and why that's a platform limitation, not a design choice
It's worth understanding why ROAS is what Google Ads shows by default, rather than treating it as an intentional choice about what matters most. Google Ads only knows what happens inside the ad platform: clicks, conversions, and the order value passed back through conversion tracking. It has no visibility into your Shopify cost data, your supplier pricing, or your margins — none of that lives anywhere Google Ads can see. Revenue is simply the only profitability-adjacent number the platform has access to, so it's what gets reported and what automated bidding strategies like Target ROAS optimise toward by default.
That's not a limitation you can configure your way out of within Google Ads alone. Value-based bidding lets you pass a custom conversion value instead of raw order value — which is how profit-aware bidding actually gets implemented in practice — but it still requires you to calculate and feed in that profit-adjusted value yourself, since Google Ads has no way to derive it independently.
Which one should you use when?
The honest answer is both, at different points in the funnel and the decision-making process — not one metric replacing the other outright.
ROAS is still useful for: early campaign diagnostics before enough conversion volume exists to trust a profit calculation, comparing creative or audience performance within a single product (where margin is constant, so ROAS and POAS move together), and communicating with anyone outside the business who thinks in revenue terms rather than margin terms.
POAS is what should drive budget decisions: which campaigns to scale, which to cut, and what your actual Smart Bidding targets should be. Any time you're deciding where the next ad dollar goes, POAS is the number that reflects what that dollar actually returns.
A reasonable default: use ROAS as a quick health check and POAS as the number you act on for budget and bidding decisions. If the two disagree meaningfully on a campaign, trust POAS — it's the one that knows what you're actually selling.
Where Shopify merchants specifically get this wrong
The most common mistake isn't picking the wrong metric — it's assuming a single account-wide ROAS target applies evenly across a catalog with mixed margins. A 4x ROAS target might be conservative for a 60%-margin product and actively unprofitable for an 18%-margin one, and Google Ads has no way to know the difference unless you tell it.
The second most common mistake is treating POAS as a nice-to-have upgrade rather than a data-pipeline problem. Calculating it once, manually, in a spreadsheet is straightforward. Keeping it accurate as prices, costs, and campaigns change every week is the part that actually breaks down — which is why most stores that "should" be tracking POAS still aren't, months after deciding it mattered.
If your catalog has meaningfully different margins across products — which describes most Shopify stores — POAS is worth the setup effort. If your margins are genuinely uniform across everything you sell, ROAS alone will track profitability closely enough that the extra complexity may not be worth it.
Not sure where your margins stand? Our break-even ROAS calculator shows the minimum ROAS each of your products needs — a fast way to see how much your break-even threshold actually varies before deciding whether POAS tracking is worth setting up. For the wider setup picture — running Google Ads profitably as a Shopify store end to end — see our complete Google Ads for Shopify guide.