The CTR formula
Worked example
A clinic's Meta ad gets 150 clicks from 10,000 impressions: a 1.5% CTR, or one click per 67 views. A new video version gets 240 clicks from the same 10,000 impressions, a 2.4% CTR. Before calling it the winner, check the A/B test calculator: at these volumes the difference is significant, but at 1,000 impressions it wouldn't be.
Reading CTR properly
Meta reports two figures: CTR (all), which counts any click including likes and expands, and CTR (link click-through rate), which counts clicks to your site. Use the link figure. On Google, compare CTR by keyword and match type rather than at campaign level, where brand terms hide the problem ones.