What is the Difference Between Email CTR and CTOR?

One standard metric used to track the performance of an email campaign is clicks, and for a good reason: most senders are not paid to send mail, or to have it opened, but for the results that come from people reading the email, often starting with clicking on a link in the email.

The most common metric used in relation to clicks is the Click-Through Rate, or CTR. The CTR is a ratio that represents how many clicks your message received relative to the number of recipients it was sent to. While various ESPs and analytics platforms will calculate this slightly differently, the most common approach is the number of unique clicks divided by the number of successfully delivered messages (meaning we remove the number of bounced messages from the send size).

It’s not uncommon for the CTR to be in the single digits percentage-wise.

A less common, but still helpful metric is the Click-To-Open Rate, or CTOR. Instead of defining the click rate relative to the size of the send, the CTOR is calculated as a ratio of dividing the number of unique clicks by the number of unique opens for a campaign. Because the number of opens is always smaller than the number of messages sent, the CTOR will always be a higher percentage than the CTR.

An Analogy

Imagine you are holding an event, and you want to get the word out, so you head to the nearest transit station exit and start handing out as many fliers as you can. In addition, you place stacks of fliers nearby in spots that people may pick up as they enter and exit the station.

Thanks to some helpful friends who were counting the number of people who went by, you know that 1,000 people passed through the exit as you were handing out fliers. You brought 300 fliers and they are all gone, so you assume that they got into the hands of people passing by, and you’re going to assume they all went to individuals, that no one two more than one flier. This is like an email open, and at 300 out of 1000 people, we’ll say it’s like a Unique Open Rate of 30%. That’s telling you how well you were able to get the attention of the people passing by similar to how your subject line works to catch your reader’s attention.

Later, you have 100 people attend your event. We’re going to think of that as a click, so 100 / 1000 people means we had a CTR of 10%, pretty good for an average campaign! But what are we measuring? The effectiveness of our ability to hand out fliers, or the effectiveness of the fliers we handed out? What if we had handed out more fliers? Would we have had even more people attend?

One way to better judge the effectiveness of the flier itself is to look at the ratio of attendees to the number of fliers we handed out, so 100 / 300, or 33% as our CTOR equivalent. This can better reflect the effectiveness of the flier itself since it determines how compelling it was.

Which Measurement Should I Use?

The truth is each metric has its own purpose, and all contribute to the whole picture:

Your Open Rate shows not only how effective your subject line was at getting people’s attention, it also serves as an indicator of how well your messages reached the inbox in the first place. Similar to how leaving a stack of fliers isn’t going to be accurate as a measure of how many wound up in people’s hands, the Open Rate is not useful as a precise measurement, but instead as a trending indicator: if the last send was 1,000 and this send is 1,500, we know the rate is up, but we don’t know that 1,500 people actually received and opened the email.

Your Click-Through Rate (CTR) shows how many people you reached actually acted on the message. This number is measurable and trustworthy: if 100 people are in the theater, we had 100 people read the flier and act on it, even if we didn’t recall handing a flier to each of them (this is why many platforms consider a click to be an implied open, where clicks will be counted as opens because how else do you see the link to click?) Where the Open Rate shows how compelling your subject line was, the click rate shows how compelling your content was, while both are affected by your deliverability.

Your Click-To-Open Rate (CTOR) factors out the number of people at the station (your deliverability) and represents only the effectiveness of your flier, because it’s only relative to the fliers you handed out. Because the Open Rate itself is inherently unreliable, the CTOR is as well, but it is helpful for understanding how well the message itself performed. The CTOR is useful for comparing the relative effectiveness of multiple campaigns if all things are equal.


Your CTR and CTOR are both helpful metrics, with the CTR being more reliable because Open Rates are inherently unreliable and the CTOR is based on Open Rate. All three metrics should be used holistically to understand your campaign performance.

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