The State of Web Vitals

Total Blocking Time (lab)

Total Blocking Time on the lab crawl.

Field data PhoneDesktopAll Scope All sites October 2026 edition · Phone field outcomes
Metric LCP INP CLS
1

At a glance the headline numbers for Total Blocking Time (lab)

Total Blocking Time on the lab crawl.

22ms
on the typical site
half of sites sit at or below
203ms
1 in 4 sites exceed this
the top quarter
6.9s
the heaviest 1%
the long tail
198,016
sites measured
phone field data

The typical site blocks the main thread for 22ms during the lab load.

The State of Web Vitals · October 2026 · 202,660 sites · phone field datacorewebvitals.io/state-of-cwv
2

Distribution & median CLS site count and median CLS at each level of total Blocking Time (lab)

0.00 0.04 0.08 0.11 0.15
0.1
0 39773 79546
0 0.01–0.038 0.038–0.143 0.143–0.541 0.541–2.04 2.04–7.73 7.73–29.2 29.2–111 111–418 418–1581 1581–5978 >p98
Good (≤0.1) Needs improvement Poor (>0.25) Site count
The State of Web Vitals · October 2026 · 202,660 sites · phone field datacorewebvitals.io/state-of-cwv
3

Passing CLS by total Blocking Time (lab) which level passes the CLS most often

Total Blocking Time (lab)SitesPassing CLSCLS
0 79,546 92% 0.00
0.01–0.038 22 81% 0.00
0.038–0.143 159 87% 0.00
0.143–0.541 457 87% 0.00
0.541–2.04 1,793 89% 0.00
2.04–7.73 6,084 90% 0.00
7.73–29.2 15,048 89% 0.00
29.2–111 29,475 88% 0.00
111–418 33,581 86% 0.00
418–1581 21,469 86% 0.00
1581–5978 8,012 85% 0.00
>p98 2,370 84% 0.00
Good Needs Improvement Poor Faded rows: under 100 sites

Total Blocking Time (lab) 22ms. p75 203ms. p99 6.9s. Spearman with CLS r = +0.30. At the low end (0ms): CLS 0.00. At the high end (>p98): CLS 0.00. computed

The State of Web Vitals · October 2026 · 202,660 sites · phone field datacorewebvitals.io/state-of-cwv
4

Why this matters for the Core Web Vitals, and where to start fixing it

Total Blocking Time counts the parts of long tasks where a click would have waited. It is the lab stand-in for INP: a crawler does not click, so instead we measure how often the main thread was too busy to answer if someone had.

High TBT with good field INP usually means real visitors interact after the dust settles. The risk lives in the early click, the visitor who taps the menu while the tag pile is still booting. The fix list is the script list: less of it, later, in smaller pieces.

How does this affect the Core Web Vitals?

Blocking time correlates with the INP. Where the blocking time is low, 92% of sites pass the INP. Where it is high, 87% do. The decline is gradual. There is no point where sites suddenly start failing. Here the relationship is causal, not just statistical.

The effect is bigger on LCP. Where the blocking time is low, 87% of sites pass it. Where it is high, 71% do.

Go fix it Yield to the main thread → 14 methods to defer JavaScript → Interaction to Next Paint →
Related signals Main-thread CPU (lab) → Lab paint timeline → Document lifecycle (lab) → Chrome field data from 202,660 sites, representing millions of real page loads · How we measured