How it works
It shows how closely the ad matched what the person was looking for. In shopping ads it depends first of all on the image, the title and the price against the competitors in the same results.
Formula
Clicks ÷ impressions × 100%
Example
The same shop: 400,000 impressions, 8,000 clicks.
CTR = 8,000 ÷ 400,000 × 100% = 2%.