In more detail
CTR measures how well a post, ad, or link convinces people to take the next step and click. You calculate it by dividing clicks by impressions, then multiplying by 100. It is the standard way to judge whether your call to action, headline, or thumbnail is doing its job, because it isolates clicks from all the other ways people engage. A low CTR usually means the content got seen but did not give people a strong enough reason to act.
Example
If a link in your post is shown 2,000 times and 40 people click it, the click-through rate is 2 percent. Swap in a sharper headline and get 80 clicks from the same 2,000 impressions, and your CTR doubles to 4 percent.
FAQ