Total Blocking Time: When a Page Feels Stuck
Total blocking time (TBT) measures how long a page blocks user input before becoming responsive. This guide explains it.
Total blocking time (TBT) measures how long a page blocks user input before responding.
What It Is
Total blocking time measures how long a page is unresponsive to user input before it becomes interactive.
It is the field metric version of interaction delays.
How It Is Measured
It sums the time the main thread is blocked during load, so it shows how long the page feels stuck.
Lower is better for responsiveness.
Why It Matters
- Blocked pages feel broken to visitors.
- Slow response pushes people away.
- It is part of the Core Web Vitals picture.
- Fixing it improves the whole experience.
How to Improve It
- Break up long running scripts.
- Defer work that is not essential.
- Cut heavy third-party scripts.
- Test responsiveness as you optimize.
The load: a visitor tries to click.
The block: the page ignores the input.
The cost: the visitor gives up and leaves.
The lesson: responsiveness is part of quality.
Quick Tip
Keep the main thread free during load, because the moment a page ignores a click is the moment a visitor leaves.
Frequently Asked Questions
Total Blocking Time (TBT), Bottom Line
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