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Gzip Size Calculator

See what your file actually weighs once it is compressed.

SEO Tools Reviews Free · no sign-up

Quick Tool Overview

The Gzip Size Calculator compresses your content in the browser and reports the real compressed size — a measurement, not a rule of thumb. It matters because the raw file size is not what crosses the wire, and an optimisation that saves 40KB of whitespace often saves almost nothing once compression has done its work.

What it does
Measures the real compressed size of text
You give it
Any text — CSS, JS, HTML, JSON
You get back
Raw and compressed sizes with the saving
Best for
Deciding whether an optimisation is actually worth doing
SEO Tools Free, unlimited use No sign-up Runs in your browser

About the Gzip Size Calculator

Paste text, HTML, CSS or JavaScript and the tool compresses it in your browser and reports the real compressed size. This is a measurement rather than a rule of thumb: the browser's own compression runs on your content and the bytes that come out are counted.

It matters because the raw file size is not what crosses the wire. Almost every server sends text compressed, so a 240KB stylesheet may be 28KB in transit, and a change that saves 40KB of raw whitespace may save almost nothing once compression has done its work — repeated whitespace is precisely what a compressor is best at. Measuring both is how you find out whether an optimisation is worth doing, and it regularly changes the answer.

Key features of the Gzip Size Calculator

A measurement, not an estimate

The browser's own compression streams run on your content and the bytes are counted.

Gzip and deflate

Both are measured, with a note on where brotli typically lands.

Before and after mode

Compress two versions to see whether a change saved anything once compression is applied.

Compression ratio

The ratio is often the more useful number — it tells you how repetitive the content is.

Nothing uploaded

Unreleased source compresses on your machine and stays there.

How to use the Gzip Size Calculator

  1. 1

    Paste your content

    Any text — a stylesheet, a script, a page, a JSON payload.

  2. 2

    Read both sizes

    The raw size, the compressed size and the ratio between them.

  3. 3

    Compare formats

    Gzip and deflate are measured; the tool notes where brotli would typically land.

  4. 4

    Test a change

    Compress before and after an optimisation to see whether it actually saved anything.

Frequently asked questions

Real. The browser's own compression streams do the work and the resulting bytes are counted. Where a browser does not support them, the tool says so rather than falling back to a guess.

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