[wp-trac] [WordPress Trac] #63018: Increase styles_inline_size_limit from 20, 000 bytes

[WordPress Trac]

#63018: Increase styles_inline_size_limit from 20,000 bytes
---------------------------+-------------------------------
 Reporter:  westonruter    |       Owner:  westonruter
     Type:  enhancement    |      Status:  accepted
 Priority:  normal         |   Milestone:  6.9
Component:  Script Loader  |     Version:  5.8
 Severity:  normal         |  Resolution:
 Keywords:                 |     Focuses:  css, performance
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Comment (by westonruter):

 This was recently
 [https://wordpress.slack.com/archives/C02KGN5K076/p1756970236447319?thread_ts=1756226698.332729&cid=C02KGN5K076
 discussed] in Slack with @aristath. The initial 20KB limit was extremely
 conservative, and it is acknowledged to be way too low.

 In my [https://weston.ruter.net/2025/08/27/the-site-speed-frontier-with-
 performance-lab-and-beyond/#minified-css-inlining research], I also found
 that on a vanilla WP install with Twenty Twenty-Five active, the
 Navigation block alone exceeds the 20KB threshold, so there is basically
 no chance that a block theme can be served without render-blocking
 stylesheets given the current limit for inlining. By increasing the
 threshold even to just 30KB, all CSS for the Sample Page can be inlined,
 and this improves LCP by 36% on an emulated Fast 4G connection and 45% on
 an emulated Slow 4G connection. I don't want to just bump to 30KB and call
 it good though, so I'm still wanting to do more digging on finding out a
 more ideal threshold based on data.

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Ticket URL: <https://core.trac.wordpress.org/ticket/63018#comment:4>
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