CTR is the number of clicks that your ad receives divided by the number of times your ad appears (called impressions). For example, if you have 5 clicks and 1,000 impressions, then your CTR is 0.5%.
CTR = Clicks on the ads ÷ Impressions (ad views)
CTR can be used to gauge how well your ads and keywords are performing. A high CTR indicates that user finds your ads relevant and useful.