How to Calculate Email Open Rate

How to Calculate Email Open Rate
Yurii Bitko Yurii Bitko 04 october 2023, 14:00 380
For experts

Open rate is one of the most essential metrics every email marketer should pay attention to. It refers to the percentage of subscribers who open your email out of the total number of subscribers. It helps you understand how engaged your subscribers are with your brand, as engaged people will likely open your messages.

This article will tell you how to measure your email open rate and how to keep it as high as possible.

What’s the point of monitoring your email open rate?

The open rate shows your level of engagement with readers. It defines the success or failure of your email campaign. A high open rate means that your subscribers are receptive to your messages and willing to read what you send to them. A low open rate shows that subscribers are disengaged with your brand, and you need to take steps to increase the rate.

Formulas to calculate email open rate

1st formula

The above formula has two variables:

  • Total recipients: the number of addresses on your mailing list.
  • Total unique opens: the number of addresses that opened your message.

Divide the total unique opens by the total recipients and multiply the result by 100 to get a percentage. For example, if you have 20 unique opens for 80 recipients, your open rate is 20/80 = 0.25. Multiply 0.25 by 100 to get 25%.

2nd formula

Some businesses prefer an advanced formula that adjusts for the number of bounced emails, i.e., the emails that didn’t make it to the intended mailboxes for whatever reason.

Let’s say you sent 80 emails, and 20 recipients opened it. But 5 emails got bounced because the addresses were unreachable. Your open rate will be (20 ÷ (80-5)) x 100. This calculation comes out to 27%.

We used the same number of total unique opens and total recipients in both formula examples. The difference is that this second formula considers the number of bounced emails, while the first does not.

The second formula is more accurate, although both will work. However, you should always stick to one formula to get results you could compare across different campaigns.

How to calculate the open rate for multiple email campaigns

You calculate the open rates for multiple campaigns by taking their average. Let’s say you’ve run four campaigns: A, B, C, and D, with the following open rates:

  • A — 20%
  • B — 25%
  • C — 30%
  • D — 15%

You could think the average of these campaigns would be 20 + 25 + 30 + 15 divided by 4. The sum of the four open rates is 90%, and 90 divided by 4 gives 22.5%.

Right? Wrong!

This approach only works with campaigns that use the same address list and have the same number of deliveries (which almost never happens). It will give you meaningless results if your mailings differ in size. Let’s assume the first three campaigns are sent to 100 subscribers each, while the fourth one is sent to 10000 addressees. The total number of letters will be 100 + 100 + 100 + 10000 = 10300, and the number of opens will be 20 + 25 + 30 + 1500 = 1575. The open rate, therefore, will be 1575 ÷ 10300 x 100 = 15.3%, which is the correct value.

The difference between open rate and click-to-open rate

Open rate deals with the number of subscribers that opened your emails. Click-to-open rate (CTOR) is the percentage of subscribers who click on a link in your email after opening it.

Click-to-open rate measures how many subscribers clicked the call-to-action button after opening your email. To calculate it, you divide the number of clicks by the number of opens (and also multiply by 100 to get the percentage). It differs from the click-through rate, which measures the percentage of subscribers that clicked on your link out of the total number of subscribers. To calculate click-through rate, you divide the number of clicks by the total number of letters sent. Marketers are increasingly shying away from click-through rates and instead focus on click-to-open rates because the latter gives a more precise view of your customer engagement.

An averag of 20% to 30% is the ideal click-to-open rate for all businesses.

How to track email open rates

The primary method of tracking email reads is by adding a tracking image to each email. Usually you do not have to care about that since your ESP does the work for you. Each time a recipient opens the email, the tracking image, aka tracking pixel, is loaded from a remote server, which counts it as an opened email.

A tracking pixel is a small image, usually 1x1 pixel in size, linked via HTML code. Because of how small it is, it’s almost impossible for the email recipient to notice it. Besides, the tracking pixels are also designed to be transparent or camouflaged in the email's background color.

The source code for a tracking image usually looks like this:

  • <img src="" width="1" height="1">

In this example, is the URL of the tracking image loaded from an external server. Whenever someone opens the email, their browser will reach the external server to download the tracking pixel. The number of such requests is taken as the number of email opens.

Tracking images are not 100% accurate. For instance, if a recipient disables images on their web browser or email client, the pixel won’t load for them, and their open event goes unnoticed. Even worse, some mailbox providers are known to block tracking pixels from loading for privacy reasons.

What factors affect email open rates?

The main factors affecting email open rates are:

  • Subject line: The subject line is the first thing an email recipient sees, and it plays a huge role in their decision to open or ignore the message. Your subject line should be engaging and personalized to get optimal results.
  • Time of delivery: The time your subscribers receive a message is also important. People are less likely to open emails at leisure time than during office hours.
  • Mobile-friendliness: Nearly half of email traffic comes from mobile phones, so your message content must be optimized to fit well on mobile displays.

Messages not optimized for mobile displays would annoy recipients reading them on a smartphone.

Example of a mobile-friendly email
Source: Really Good Emails
  • Spam complaints: If your domain or IP address has a high spam complaint rate, your emails might not reach the intended recipients. They’ll land in the spam folder instead of the main inbox.
  • Subscriber list quality: The quality of your mailing list affects the open rates. Your open rate will likely be high if you have a legitimate list of opt-in addresses. In contrast, if you purchased a mailing list, your open rate will be low because the addresses didn’t opt-in to receive your messages, and you will likely be blacklisted for spam.
  • Seasonal and holiday factors: Open rates often decline during seasonal periods and celebrations, e.g., Christmas, Easter, and Halloween. This happens because there’s heightened competition for businesses to sell stuff to customers during these periods; consumers receive more emails than usual and are more picky about which ones they open.
  • Recipient’s device: People are more likely to open your messages if they receive them on a mobile device than on a desktop.

Steps to improve your email open rate

You can employ the following methods to improve your email open rate:

Use a proper sender name

The sender name is the first thing your recipient sees along with the subject line. Hence, you should use a name with which people can easily identify your brand.

Don’t use a generic name such as Acme Support Team or Technical Crew. A personal touch works better, so use something like Bob from Acme Support and Jane from Technical Crew. Personalized sending names can improve your open rates by a significant margin.

It’s advisable to include your brand logo in your emails. Many popular email clients now support Brand Indicator for Message Identification or BIMI, a standard that lets businesses use logos to authenticate their brand identity. The brand logo ownership is verified with a digital certificate, so recipients can be sure they’re receiving a message from you and not an impersonator.

Example of email senders using Brand Indicator for Message Identification (BIMI).

Use an engaging subject line

We have already mentioned that the subject line plays a vital role in a recipient’s decision to open or ignore a message. You should use engaging subject lines to increase your open rates as much as possible.

A good subject line should be:

  • Precise: The recipient should be able to understand the message from a quick glance at the subject line; this helps them make a fast decision whether to open it. The optimal length for a subject line is 60 characters or 9 words.
  • Relevant: It should contain information that’s relevant to your audience. For instance, if you’re an electronics retailer, your subject line should stick to that area. Avoid subject lines that don’t relate to your line of business.
  • Personalized: It should include something for the recipient to feel important. You can start with something like “Dear [Recipient’s First Name]” or ”Hello [Recipient’s First Name]” etc.
  • Urgency: you can use language that creates a sense of urgency, e.g., “Act fast,” “Last chance,” “Hurry,” etc. Be sure to test this option, however, as it increases the risk of getting into spam.


Segmentation entails separating your mailing list into different categories so that you can send more targeted messages. For example, you can segment your list according to recipients’ ages:

  • Segment A: 18-24 (Gen Z).
  • Segment B: 25-40 (Millennials).
  • Segment C: 65 and older (Seniors).

After segmenting your lists, you can use different approaches to market products to each one. For example, you can use popular slang in segments A and B because the younger cohort is more familiar with it. You’ll use formal language for list C because the Senior cohort is less likely to welcome informal wording.

The idea of segmenting your list is to create content each segment will appreciate better. This way, they’ll be more receptive to your messages and more willing to open new ones.

How to test emails to get better sending rates

It’s advised to test your emails before sending them en masse if you want to get the best results.

You can run a spam test by first sending the message to a small number of addresses you’re familiar with; they could be your friends and family. Check what percentage of them received your message and what percentage, if any, find the email in their spam folders. This test gives you a good idea of whether your emails will land in the primary inboxes when you send them en masse.

You should preview your email content on mobile and desktop screens. Check if the text and graphics are displayed correctly on different displays, email clients and platforms. Check if the subject line is visible on different screens. Once you’re sure everything is ok, you can proceed with your campaign.

Above all, opt for a good email service provider (ESP) like UniOne. No matter how well-optimized your emails are, choosing an unreliable ESP means that many will not reach the intended recipients. Luckily, UniOne is a secure and reliable email service provider that you can trust.

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