What is CTR?
CTR (click through rate) is the share of people who click an ad after seeing it.
CTR shows how relevant and attractive your ad is for the people who see it. On Google Search it is typically several percent, on Meta often around 1 %.
Higher CTR usually lowers your cost per click on Google, because relevance is part of the auction.
Formula
CTR = clicks / impressions x 100
Example
Your ad was shown 2,000 times and clicked 100 times. CTR is 5 %.