Ads Fundamentals
How ad auctions actually decide who wins, and the six numbers that tell you whether you are winning.
You are not bidding against other advertisers
Every impression on Meta or Google is decided by an auction, but the highest bid does not win it. Both platforms rank competing ads by a combination of your bid and how likely the platform thinks the person is to do what you asked for. A cheap bid on an ad people actually engage with routinely beats an expensive bid on an ad they ignore.
This is why "raise the bid" is almost never the first fix. The bid is one of three inputs, and it is the only one that costs you money directly.
| Platform | What it ranks on |
|---|---|
| Meta | Total value — your bid, estimated action rate (how likely this person takes your optimisation event), and ad quality |
| Ad Rank — your bid, ad quality including expected CTR and landing page experience, context of the search, and expected impact of assets and formats |
Practical read: if your costs are climbing, check the estimated-action-rate side of the equation — creative, audience match, landing page speed — before you touch budget.
The six numbers
Every ads conversation eventually reduces to these. Learn the formulas, not the dashboard labels — platforms rename columns constantly, but the arithmetic never changes.
| Metric | Formula | What moves it |
|---|---|---|
| CPM | (spend / impressions) × 1000 | Audience competitiveness, placement, season |
| CTR | clicks / impressions | Creative and offer relevance |
| CPC | spend / clicks | CPM and CTR together |
| CVR | conversions / clicks | Landing page, offer, traffic quality |
| CPA | spend / conversions | CPC and CVR together |
| ROAS | revenue / spend | CPA and average order value together |
CPA and ROAS are outcomes, not levers. You cannot "fix CPA" — you fix CPC or CVR, and CPA follows. Knowing which of the two is broken is most of diagnosis.
Breakeven ROAS, the number that decides everything
A 3× ROAS is excellent for one business and bankruptcy for another. What matters is where your breakeven sits, and that comes from your margin, not from a benchmark.
breakeven_roas = 1 / gross_marginAt a 40% gross margin, breakeven is 1 / 0.40 = 2.5×. Every point of ROAS above 2.5 is profit; a campaign at 2.2× is losing money while showing a "positive" return. Work this out before you launch, and write it at the top of the reporting sheet.
- Know your gross margin after cost of goods, shipping and payment fees.
- Compute breakeven ROAS once, per product line if margins differ.
- Compare campaigns to breakeven, never to someone else's screenshot.
Reported results are not incremental results
Platforms report the conversions they can attribute to themselves, inside their own attribution window. That number includes people who would have bought anyway. It is useful for comparing your own campaigns against each other, and misleading when read as profit.
- Use platform numbers to compare ads and audiences within the same platform and window.
- Use your own backend revenue as the source of truth for what the business earned.
- Expect the two to disagree. The gap itself is a signal, not an error to be fixed.
Adding up conversions across Meta, Google and GA4 will double-count. Two platforms both claiming the same sale is normal, not fraud.
Features covered here
Check your understanding
3 questions. Wrong answers explain themselves.
1.Your CPA doubled this week while CPM stayed flat. Where do you look first?
CPA is spend / conversions, which decomposes into CPC and CVR. With CPM flat, the cost of reaching people did not change — so either fewer people are clicking (CTR) or fewer clickers are converting (CVR). Bidding and duplicating treat symptoms without identifying which.
2.Your gross margin is 25%. What is your breakeven ROAS?
Breakeven ROAS is 1 / gross margin, so 1 / 0.25 = 4×. Anything below 4× loses money even though the platform reports a positive return.
3.Meta reports 100 purchases and Google reports 60, but your store recorded 130 orders. What is the most likely explanation?
Each platform attributes conversions it believes it influenced, within its own window, with no knowledge of the other. Overlap is expected. Your backend order count is the source of truth for the business; platform numbers are for comparing campaigns inside each platform.