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CSS Payload Calculator

Assess CSS payload size and the saving from removing unused rules.

About CSS Payload Calculator

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.

Formula

CSS Payload

Blocking time = compressed CSS ÷ bandwidth + one round trip

render blocking
CSS must load before first paint unless split into critical and deferred

Worked example

With the default values below, CSS Payload Calculator returns Render-Blocking Time of 124. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total CSS sizeminimum 0 KB
320 KB
Share of rules unused on the pageaccepts 0–100 %
65 %
Compression savingaccepts 0–100 %
75 %
Connection speedminimum 0.01 Mbps
10 Mbps
Round-trip latencyminimum 0 ms
60 ms

Results

Render-Blocking Time
124 ms
Compressed Size
80.00 KB
CSS Actually Used
112.00 KB
Time Saved by Removing Unused CSS
42 ms
Verdict
Most CSS is unused — purging would substantially cut blocking time

Step by step

  1. 1Values used
  2. 2CSS Payload
  3. 3Render-Blocking Time= 124 ms
  4. 4Compressed Size= 80.00 KB
  5. 5CSS Actually Used= 112.00 KB
  6. 6Time Saved by Removing Unused CSS= 42 ms
  7. 7Verdict= Most CSS is unused — purging would substantially cut blocking time

Assumptions and limits

  • The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is CSS Payload calculated?

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.

Why does CSS Payload matter?

Utility and component frameworks commonly leave 60 to 90 per cent of rules unused on any single page, which purging tools can remove automatically.

What values do I need to enter?

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.

Related Calculators

CSS Payload Calculator – Calculate Render-Blocking Time