{"id":333,"date":"2023-03-15T08:20:20","date_gmt":"2023-03-15T08:20:20","guid":{"rendered":"https:\/\/rabbitloader.com\/articles\/?p=333"},"modified":"2025-04-03T04:58:37","modified_gmt":"2025-04-03T04:58:37","slug":"total-blocking-time","status":"publish","type":"post","link":"https:\/\/rabbitloader.com\/articles\/total-blocking-time\/","title":{"rendered":"What Is Total Blocking Time (TBT) & How to Optimize It to Boost The PageSpeed Score?"},"content":{"rendered":"\n

You may have encountered the term Total Blocking Time (TBT) while analyzing your PageSpeed performance in Google PageSpeed Insights or GTmetrix. But what is Total Blocking Time?<\/p>\n\n\n\n

Google added this Total Blocking Time (TBT) metric to its PageSpeed & lighthouse tests to analyze the span of time when the main thread is blocked and the user needs to wait to see the website\u2019s content.<\/p>\n\n\n\n

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Google PageSpeed Insights considers TBT along with four other metrics to determine the PageSpeed score. <\/p>\n\n\n\n

Here, you\u2019ll learn everything you need to know about Total Blocking Time (TBT) and how you can easily optimize your TBT performance by using RabbitLoader without needing coding skills. <\/p>\n\n\n\n

<\/span>What Is Total Blocking Time (TBT)?<\/span><\/h2>\n\n\n\n

Total Blocking Time (TBT) accounts for 30% of the overall Google PSI score. This performance metric is used to analyze the load responsiveness of a website. In simple words, TBT measures the span of time, a long task (which takes more than 50 ms ) blocks the main thread and negatively affects your page\u2019s usability. <\/p>\n\n\n\n

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Let\u2019s understand TBT with an example. Assume, there are a total of 4 tasks in which task 1 takes 150 ms, task 2 takes 30 ms, task 3 needs 100 ms, and finally, task 4 requires 350 ms.The TBT for these 4 tasks combines would be 450 ms (100+50+300).<\/p>\n\n\n\n

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Task <\/strong><\/td>Time Required (in milliseconds )<\/strong><\/td>Blocking time (in milliseconds )<\/strong><\/td><\/tr>
Task 1<\/td>150<\/td>(150-50)= 100<\/td><\/tr>
Task 2<\/td>30<\/td>Not considerable <\/td><\/tr>
Task 3<\/td>100<\/td>(100-50)= 50<\/td><\/tr>
Task 4<\/td>350<\/td>(350-50)= 300<\/td><\/tr>
<\/td>Total required time= 630 ms<\/strong><\/td>Total Blocking Time= 450 ms<\/strong><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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<\/span>How To Measure Total Blocking Time?<\/span><\/h2>\n\n\n\n

You already understand how Total Blocking Time is calculated. Here we will mention the helpful tools to measure the Total Blocking Time. There are several tools available to measure TBT. Let’s discuss the two most popular online tools to measure it.<\/p>\n\n\n\n

<\/span>Google PageSpeed Insights<\/span><\/h3>\n\n\n\n
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Google PageSpeed Insights considers 5 web performance<\/a> metrics to determine the PageSpeed score. Among these 5 metrics, TBT is one of them. To know how to measure it in Google PageSpeed Insights, read our PageSpeed Insights blog.<\/p>\n\n\n\n

<\/span>GTmetrix <\/span><\/h3>\n\n\n\n

GTmetrix is the best alternative tool for measuring PageSpeed performance. Its advantage over Google PSI is that it allows customizing the test location and device. For more details, read our post on GTmetrix.  <\/p>\n\n\n\n

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<\/span>What Is An Ideal Total Blocking Time?<\/span><\/h2>\n\n\n\n

In order to categorize the performance of Total Blocking Time (TBT), google sets some boundary values. To be in a green zone, your Total blocking Time should be less than 300 ms for the whole page Let’s explore the criteria.<\/p>\n\n\n\n

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TBT time (in milliseconds)<\/strong><\/td>Status<\/strong><\/td>Color <\/strong><\/td><\/tr>
Less than 300 ms<\/td>Good<\/td>Green<\/td><\/tr>
In between 300 ms to 600 ms<\/td>Moderate (need to improve)<\/td>Orange<\/td><\/tr>
More than 600 ms <\/td>Poor<\/td>Red <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

<\/span>The Reason Behind A High Total Blocking Time<\/span><\/h2>\n\n\n\n

Before discussing the solution, it\u2019s important to know the reason behind a high TBT. Let’s explore the most common causes that can inflate the Total Blocking Time (TBT).<\/p>\n\n\n\n