Measurement
The ad metrics that matter, with formulas
Ten numbers cover most of what you need to read an ad account. Here is what each one is, how it is worked out, and what it is good and bad at telling you.
Read these in order. Each one sits a step further down the path from someone being shown an ad to money arriving.
Reach and attention
CPM
Cost per thousand impressions: the price of being seen. It reflects competition, audience and season more than the quality of your ad, so a rising CPM is not always your fault.
Frequency
The average number of times each person has seen your ad. When frequency climbs and results fall, the audience has likely seen enough of that creative.
CTR
Click-through rate: the share of impressions that became a click. Check which version you are reading. Meta shows one CTR for all clicks on the ad and another for link clicks only, and the second is the one that matters.
Cost and conversion
CPC
Cost per click. Useful for comparing ads, but cheap clicks from people who never convert are not a bargain.
Conversion rate
The share of clicks that became a lead, sale or donation. This is mostly a measure of your landing page and offer, not your ad.
CPA
Cost per acquisition. Also called cost per lead, cost per purchase or cost per donation, depending on what you count. This is the number most campaigns should be judged on.
Return
ROAS
Return on ad spend, as reported by one platform. A ROAS of 4 means 4 back for every 1 spent, according to that platform's attribution. It is useful for comparing campaigns and unreliable as a statement of what you earned.
MER
Marketing efficiency ratio, sometimes called blended ROAS. It uses your real revenue from all sources, so no platform can inflate it. Watch it alongside platform ROAS.
Average order value
For a charity this is the average gift. Raising it, through suggested amounts or bundles, improves every return figure without spending more.
Lifetime value
What a customer or donor is worth over the whole relationship. A monthly donor acquired at a cost that looks high against their first gift may be very good value over a year.
How they fit together
These numbers are links in one chain. If cost per acquisition rises, walk back up it. Did CPM rise, so you are paying more to be seen? Did CTR fall, so the creative has tired? Did conversion rate fall, so something changed on the page? The answer tells you which thing to fix.
One warning. Every figure here except MER depends on what the platform managed to track and how it attributes credit. Read our guides on attribution and tracking setup before trusting them to the decimal.
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