Plain answer
An impression is one display of your ad. Reach is how many different people saw it. Frequency is impressions divided by reach — how many times the average person saw the ad. High frequency with flat results means you're paying to show the same people an ad they've already ignored.
How the three numbers relate
The math is one division: frequency = impressions ÷ reach. Show your ad 10,000 times to 2,500 people and your frequency is 4 — the average person saw it four times.
Each number answers a different question. Impressions tell you how much the platform delivered. Reach tells you how many humans that delivery actually touched. Frequency tells you whether you're meeting new people or wearing out the same ones. Platforms report impressions most prominently because it's the number that always goes up when you spend more.
What's a good frequency?
It depends on what the ad is for. A retargeting ad reminding warm prospects can stand a higher frequency — they know you, and buying decisions take repeated nudges. A cold-audience ad climbing past a frequency of 3–4 with no lift in CTR or conversions is usually a sign the audience has seen it, judged it, and moved on.
The pattern to watch is direction, not a magic number: frequency rising while results stay flat means the platform has run out of new people to show your ad to at your budget. That's when you refresh the creative, widen the audience, or stop paying for reruns.
What this means for your ads
Don't celebrate impressions — anyone can buy views. Check reach to see how many real people your budget touched, then check frequency to see whether the next dollar buys a new prospect or a repeat showing. When frequency climbs and results don't, the ad isn't underperforming — it's finished. Retire it before the spend quietly turns into wallpaper.
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