CTR, or click-through rate, refers to the percentage of users who click on an ad out of the total number of users who simply view the ad. It’s a key metric used to measure the effectiveness and appeal of any ad across all digital media, including mobile. 

To calculate CTR, divide the number of clicks an ad receives by the number of times it’s shown (impressions), then multiply the result by 100 to get a percentage. So, if an ad is displayed 1,000 times and gets 10 clicks, the CTR would be (10/1000) * 100 = 1%.

Because it provides insight into how well an ad captures the attention of its audience, CTR is an important metric. A higher CTR is reliable evidence that a campaign is on track: the right audience has been targeted, and the creative is relevant and engaging to them. A lower CTR might mean that either the creative or the audience needs adjusting.