Email marketing metrics explained

One of the best things about email marketing is that it can be so easily tracked, measured and reported on. You know exactly what’s going on. What do your subscribers love? What do they not like quite as much? What really drives clicks and what falls flat? With simple and easy tracking, you have insight into these questions and so much more. You’ll know exactly where the conversions have happened and you’ll be able to identify areas for improvement.


The key metrics to measure are:

  1. Send volume
  2. Bounce number
  3. Delivery rate
  4. Open rate (total & unique)
  5. Click through rate (CTR)
  6. Click to open rate (CTO)
  7. Conversion rate
  8. Revenue per email
  9. Unsubscribe rate

Send volume

The total count of recipients (email addresses) that were sent the email message. This is the final count after all recency and suppressions have been applied. 


Bounce number

This is the number of email addresses that bounced back from the ISPs (Gmail, Outlook, Yahoo etc.) There are two types of bounce:


- Hard bounce number - A permanent bounce when the email address is invalid. An email address may be invalid if if does not exist. Hard bounces should be set to a do not email setting on the first bounce occurrence.


- Soft bounce number - A temporary bounce usually due to a full inbox of ISP deferring. Attempt to send to these emails 2-3 times before moving to a 'do not email' setting.


How to calculate bounce rate:


To calculate the percentage of your total emails that were not successfully delivered use this calculation:



Delivered number and percentage

The total number of emails successfully delivered to the inbox.

Send Volume - Total Bounces = Number of emails delivered

As a percentage, delivery rate should be around 95% or higher. To calculate as a percentage:




Open rate

The open rate is the percentage of recipients that have opened your email compared to how many contacts were sent the email.


The open rate can be split into total opens (the total number of opens for the email e.g. an email address may open the email 3 times which equals 3 opens) and unique opens (the number of unique opens for the email e.g. if an individual email address opens the email 3 times, that equals 1 unique open).


The percentage of total opens is calculated by:




The percentage of unique opens is calculated by:




On average, open rates should be between 15-30% depending on level of segmentation and type of email message.


How are opens tracked?

An open is recorded by an invisible 1x1 GIF in the email HTML creative when the recipient downloads images. The GIF is added automatically by your ESP.


Using open rate

Tracking the open rate is really handy if you are split testing subject lines as it gives you the metrics you need to understand which version performed best. It's also a good metric to track over time to measure success; if the open rate increases over time, subscribers are enjoying the content you are sharing.


Click through rate (CTR) 

Click through rate is the percentage of recipients that have clicked on any link in your email. Clicks are tracked in your ESP via tracking code appended to the end of links. Click through rate is calculated using this formula:




Click to open rate (CTOR / CTO)

CTO rate tells you out of the subscribers that opened the email, how many of them clicked. It is an important metric to use when considering content relevancy - if the CTO rate is higher, the content in the email is relevant to the people opening and they respond by clicking through. Open rates can vary so CTO is a useful measurement of content and creative to compare across campaigns.




Conversion rate

Conversion rate is the percentage of email recipients that clicked on a link in your email and then went on to complete a desired action. For example, if a recipient clicked on a 'Shop Now' CTA in your email and then made a purchase on your website, they have completed the desired action. They have converted from your email.


When calculating conversion rate it is important to define your end goal e.g. is it a purchase on site or a content download? Then you need to decide whether to base your conversion rate on all sent emails, the number of emails opened, or should you only consider emails clicks e.g. from the number of clicks in email, how many went on to convert. Once you have these defined you can use this calculation:




If using the send volume in this calculation, expect the conversion rate to be low.


Revenue per email

Calculating revenue should be a high priority. It is important to know the overall return on investment for each email. 




Unsubscribe rate

The unsubscribe rate is the percentage of recipients that unsubscribe from your email. This includes recipients that click on your unsubscribe link in the email and those that unsubscribe via the list unsubscribe option in the inbox.




Your unsubscribe rate should always be less than 1%.


Whilst these are the most widely used metrics, there are some additional metrics to consider:

  • List growth rate
  • Spam complaint rate

List growth rate

This is how to measure the rate of your email list growth over time.




It is important to keep track of list size and any growth or loss of subscribers. The goal should always be to increase your list size but there will always be some natural list decay. It's important to keep an eye on this and to measure it make sure your list size remains healthy.


Spam complaint rate

Spam complaint rate is the percentage of recipients that click the spam or junk button in their inbox. Spam complaints are recorded via feedback loops provided by the ISPs.




Your spam complaint rate should always be less that 0.1%.



Taking these measurements and putting them into a report is the first step to effectively measuring email marketing performance. Measure and report on each email and then track results over time to get a clear picture of effectiveness.


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