If you're running Google Ads for your Shopify store, you're almost certainly measuring Return on Ad Spend (ROAS). Your agency reports it. Google's Smart Bidding optimises for it. It feels like the right number.
It isn't.
What ROAS actually tells you
ROAS measures revenue generated per pound (or dollar) spent on ads. A ROAS of 4 means for every £1 you spend, you generate £4 in revenue. Sounds great.
But revenue isn't money in your pocket. Your products have costs — cost of goods, fulfilment, payment processing, returns. A product with a 20% margin at 4x ROAS is generating £0.80 in gross profit for every £1 spent on ads.
You're losing money on every click.
Introducing Profit on Ad Spend (POAS)
POAS is a simple concept: how much profit do you generate for every pound spent on ads?
POAS = (Revenue − Cost of Goods) ÷ Ad Spend
A POAS of 1.0 means you break even. Anything above 1.0 means you're generating profit from your ad spend. The higher, the better.
Why ROAS hides unprofitable campaigns
Consider two campaigns:
| Campaign | Spend | Revenue | ROAS | Margin | Profit | POAS | |---|---|---|---|---|---|---| | A | £1,000 | £5,000 | 5x | 15% | £750 | 0.75 | | B | £1,000 | £3,000 | 3x | 45% | £1,350 | 1.35 |
Campaign A has the better ROAS. If you're optimising for ROAS, you'll scale Campaign A and cut Campaign B.
But Campaign A is destroying value. You're spending £1,000 to generate £750 in gross profit — a net loss of £250 per £1,000 spent, before accounting for any other overheads.
Campaign B is the one worth scaling. Its lower ROAS hides a genuinely profitable campaign.
This pattern plays out across thousands of Shopify stores every day.
The problem with switching to POAS manually
Calculating POAS requires connecting your Google Ads spend data with your actual product margins. For most merchants, that means:
- Exporting Google Ads spend by campaign
- Matching campaigns to the products they sell (not always obvious)
- Looking up COGS for those products in Shopify
- Building a spreadsheet that breaks the moment a product price changes
Most merchants don't do this. The ones that do spend hours on it every week.
What changes when you optimise for POAS
When you switch your decision-making from ROAS to POAS, a few things happen:
You stop scaling unprofitable campaigns. High-ROAS, low-margin campaigns stop looking like winners.
You find hidden gems. Low-ROAS campaigns selling high-margin products often become your best performers once you account for profit.
Your ad budget compounds. Every pound reallocated from a POAS < 1 campaign to a POAS > 1 campaign directly improves profitability.
You can set a real target. Instead of an arbitrary ROAS target (why 4x and not 3.5x?), you can set a POAS target based on your actual cost structure.
How Selvra OS automates this
Selvra OS connects directly to your Shopify store and Google Ads account. It pulls your product margins (from Shopify metafields, category averages, or a flat margin you set) and automatically calculates POAS for every campaign, every day.
When a campaign drops below your POAS threshold, the agent proposes a specific action — reduce budget, pause the campaign, add negative keywords — with a plain-English explanation of why. You approve or reject it. Nothing changes without your sign-off.
No spreadsheets. No manual data wrangling. Just clear, profitable decisions.
Selvra OS is currently in early access for Shopify merchants spending £3k–£50k/month on Google Ads. Get early access →