Assess CSS payload size and the saving from removing unused rules.
CSS is render-blocking by default, so its full size delays first paint even if most rules are unused on that page. Extracting critical CSS and deferring the rest removes most of the delay. Utility and component frameworks commonly leave 60 to 90 per cent of rules unused on any single page, which purging tools can remove automatically.
CSS Payload
Blocking time = compressed CSS ÷ bandwidth + one round trip
Blocking time = compressed CSS ÷ bandwidth + one round trip CSS is render-blocking by default, so its full size delays first paint even if most rules are unused on that page. Extracting critical CSS and deferring the rest removes most of the delay.
Utility and component frameworks commonly leave 60 to 90 per cent of rules unused on any single page, which purging tools can remove automatically.
This calculator takes 5 inputs: Total CSS size, Share of rules unused on the page, Compression saving, Connection speed, Round-trip latency. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.