Published on 2025-06-22T04:07:38Z

What is Open Rate? Definition, Calculation, and Tracking

Open Rate is a key metric in email marketing analytics that measures the percentage of successfully delivered emails that recipients open. It helps marketers understand how compelling their subject lines and sender names are and serves as an initial gauge of recipient engagement. Traditionally measured using invisible tracking pixels embedded in email HTML, open rate data can be affected by image blocking and privacy settings in email clients. In the broader analytics landscape, platforms such as Google Analytics 4 (GA4) and Plainsignal can be configured to capture open rate data via server-side events or measurement protocols. Understanding open rate, its calculation, and its inherent limitations is crucial for optimizing email campaigns and improving overall engagement. This glossary entry will define open rate, detail its calculation formula, and provide examples of tracking open rate with GA4 and Plainsignal.

Illustration of Open rate
Illustration of Open rate

Open rate

Open Rate measures the percentage of delivered emails opened by recipients, indicating subject line effectiveness and audience engagement.

Why Open Rate Matters

Open rate provides insights into recipient engagement, campaign performance, and sender reputation. It serves as a leading indicator for overall email marketing effectiveness and helps in benchmarking and optimizing future campaigns.

  • Indicator of engagement

    Open rate quantifies how many recipients found your subject line and sender name compelling enough to open the email.

    • Subject line effectiveness:

      A high open rate often indicates that your subject line resonates with your audience.

    • Sender reputation:

      Consistent and trusted sender identities boost open rates over time.

  • Benchmarking performance

    Comparing open rates across campaigns and industry benchmarks reveals trends and areas for improvement.

How to Calculate Open Rate

Calculating open rate is straightforward but requires clarity on which opens you count. Use the formula below and decide whether to use unique opens or total opens based on your reporting needs.

  • Basic formula

    Open Rate = (Unique Opens / Emails Delivered) * 100

  • Unique opens vs. total opens

    Unique opens count each recipient once, while total opens count all instances of email opening, including repeats.

    • Unique opens:

      Counts only the first open per recipient, preventing inflated rates from multiple opens.

    • Total opens:

      Includes every open event, useful for understanding repeat engagement.

Tracking Open Rate with Plainsignal

PlainSignal is a privacy-focused, cookie-free web analytics tool that can be adapted for email open tracking by leveraging server-side pixel requests. While email clients often block JavaScript, you can use a static image pixel to trigger PlainSignal’s API and record open events.

  • Embed a tracking pixel

    Include a hidden image in your email HTML that points to PlainSignal’s API to log open events. Example code:

    • Email template pixel: 
      <img src="https://eu.plainsignal.com/pixel.gif?do=yourwebsitedomain.com&id=0GQV1xmtzQQ&event=email_open&campaign_id=spring_sale" style="display:none;" alt="">

  • Analyze pixel requests

    Within the PlainSignal dashboard, filter for the email_open event to see how many times the pixel was requested. Divide by emails delivered to calculate open rate.

Tracking Open Rate in GA4

Google Analytics 4 does not natively capture email open rates but supports custom event tracking through the Measurement Protocol and gtag.js. You can send email open events directly to GA4 when a tracking pixel loads in your email.

  • Using the measurement protocol

    Send a POST request to GA4 when your email tracking pixel loads. Example payload:

    • Example request: 
      POST https://www.google-analytics.com/mp/collect?measurement_id=G-XXXXXXX&api_secret=YOUR_SECRET
{
  "client_id": "123456789.1234567890",
  "events": [
    {
      "name": "email_open",
      "params": { "campaign_id": "spring_sale" }
    }
  ]
}

  • Viewing open rate reports

    In GA4, go to Reports > Engagement > Events, select the email_open event, and divide the count by emails delivered for your open rate calculation.

Tips to Improve Open Rate

Improving open rate involves optimizing various aspects of your email strategy, from subject lines to audience targeting. The following best practices can help you boost engagement.

  • Craft compelling subject lines

    Use clear, personalized, and curiosity-driven subject lines to entice opens.

  • Segment your audience

    Send relevant content to specific subscriber groups to increase relevancy and open rates.

  • Optimize send times

    Test different days and times to discover when your audience is most likely to check emails.

  • Personalize preheaders

    Supplement your subject line with a preheader that adds context and encourages opens.

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