Six numbers cover most of what an ad account is telling you. The trick is not memorising the definitions — it is knowing which one to look at first, because they are arithmetically linked and a change in one shows up in all of them.
The six
ROAS — return on ad spend. Revenue ÷ spend. Answers "did the money come back". Only meaningful against your own break-even ROAS.
CPA — cost per acquisition. Spend ÷ customers. The same question as ROAS in a shape that survives when order values vary.
CPL — cost per lead. Spend ÷ leads. Only a cost of a customer once you divide by the close rate.
CTR — click-through rate. Clicks ÷ impressions. Mostly a verdict on the creative and the match between the ad and who saw it.
CPM — cost per thousand impressions. What the auction charges you to be seen. Moves with competition, audience and season — largely a market price rather than a skill score.
Frequency. Impressions ÷ reach over a window. How many times the average person saw it.
How they connect
The relationships are worth internalising, because they turn a vague "performance is down" into a diagnosis:
CPC = CPM ÷ (CTR × 1,000)
CPA = CPC ÷ conversion rate
ROAS = average order value ÷ CPA
Read that chain backwards and every ROAS problem is one of four things: order value fell, conversion rate fell, click cost rose, or you are buying worse clicks.
The order to check in
When results drop, go down this list rather than staring at ROAS:
- Frequency. Climbing hard while CTR falls is the classic fatigue signature. Fix: new creative, not a budget change.
- CTR. Down on its own, with frequency flat? The creative or the audience match is off.
- CPM. Up while CTR held? You are paying more for the same attention — competition, seasonality, or a narrowed audience.
- Conversion rate. Clicks steady but conversions down? The problem is after the click: the page, the offer, the stock, or your tracking.
- Average order value. Quietly falling AOV drags ROAS down while every ad metric looks fine.
Most accounts skip to step three and change budgets, which is the one lever that does not fix any of the first four.
Two metrics that mislead
Impressions. A big number that goes up when you spend more. It measures purchase volume, not performance.
Platform-reported conversions across channels. Each platform claims what it can attribute. Adding two platforms' claims together double-counts customers who saw both — see why Meta-only reporting flatters you.
A note on benchmarks
Published benchmarks for CTR and CPM are averages over wildly different businesses, and using them to grade your account tells you mostly about your industry and your country. The comparison that works is your own account over time, and the only absolute line is your break-even ROAS.
Compute them from one set of numbers
The ad metrics calculator takes spend, impressions, clicks, conversions and revenue and prints all of the above, graded against the break-even you supply. It uses the same formulas the app does, runs in your browser, and stores nothing.