01
ZIP File Creator
Packs any set of files into a single .zip archive inside your browser, with a choice of…
Gzip Size Estimator
Measures the real gzipped size of CSS, JS, HTML or JSON and shows the transfer time saved across typical connection speeds.
Developer
Nothing uploaded
No sign-up
Free, unlimited
Drop a CSS, JS, HTML or JSON fileor paste the code below — measured, not estimated
Add a file to begin.
In short
Gzip Size Estimator is a free online tool on inputtesthub.com that measures the real gzipped size of CSS, JS, HTML or JSON and shows the transfer time saved across typical connection speeds. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.
How to use the Gzip Size Estimator
- Drop the file, or paste the code.
- Read the gzipped figure, not the size on disk.
- Use the connection table to turn bytes into milliseconds.
About the Gzip Size Estimator
The Gzip Size Estimator measures the real gzipped size of CSS, JS, HTML or JSON and shows the transfer time saved across typical connection speeds. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Quoting a real number in a performance budget.
- Checking whether a library is worth its transfer cost.
- Showing that a 300 KB bundle is 80 KB over the wire.
Details
| Method | Actually compressed with the browser's gzip, not estimated |
|---|---|
| Also shows | Raw deflate, which is gzip minus its 18-byte wrapper |
| Typical text saving | 60–80% for CSS, JS, HTML and JSON |
| Brotli | Usually a further 15–20% — not measurable here |
Comparing two libraries on disk size is close to meaningless. One may be verbose and highly repetitive and gzip beautifully; another may be dense and barely shrink at all. This measures the number the visitor actually downloads.
Where this tool stops
Measures gzip and raw deflate only. Real transfer also carries HTTP headers and, over HTTP/2, shares a compression context between requests — both small effects, neither modelled.
Frequently asked questions
Which number should I put in a performance budget?
The gzipped one. Any server worth using compresses text before sending it, so the size on disk is not what a visitor waits for. Quoting the uncompressed figure is the commonest way a performance budget ends up two or three times stricter than it needs to be.
My CDN uses Brotli. Is this still useful?
Yes, as a floor. Brotli typically beats gzip by 15–20% on text, so the real transfer will be a little smaller than shown. It cannot be measured here because the browser's compression API has no Brotli format and this page deliberately ships no library.
Why does minifying barely change the gzipped size?
Because the two remove the same redundancy. Minification strips whitespace and shortens names; gzip was already encoding all that repeated whitespace in a handful of bits. Minifying still helps — just far less on the wire than the file size suggests.
Do I need an account to use the Gzip Size Estimator?
There is no cost and no cap. The Gzip Size Estimator is not a demo of a paid product, so nothing is held back or watermarked.
Is my data uploaded anywhere?
No. The Gzip Size Estimator runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
What problem does the Gzip Size Estimator solve?
Typical uses: quoting a real number in a performance budget. Checking whether a library is worth its transfer cost. Showing that a 300 KB bundle is 80 KB over the wire. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything the Gzip Size Estimator cannot do?
Measures gzip and raw deflate only. Real transfer also carries HTTP headers and, over HTTP/2, shares a compression context between requests — both small effects, neither modelled. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What figures does the Gzip Size Estimator work from?
Method is Actually compressed with the browser's gzip, not estimated. Also shows is Raw deflate, which is gzip minus its 18-byte wrapper. Typical text saving is 60–80% for CSS, JS, HTML and JSON. These are printed on the page itself, so you do not have to take them on trust.
How large a file can I use?
There is no limit set by us, because your file is never uploaded — the only ceiling is the memory your own browser will give the tab. Very large files simply take longer to process, and a phone will give up sooner than a desktop.
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