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GZIP compressor

Compress a file locally with fast, balanced or smallest GZIP settings and compare the resulting file size.

Choose a file

Choose a file to get started, or drag and drop it here.

Up to 16 MiB

Compress one file with GZIP. Choose a balance of speed and file size.

How it works & useful details

Compress one file with GZIP. Choose a balance of speed and file size.

Everything runs locally. Files are never uploaded. Maximum 16 MiB per input file, 32 MiB combined, and 1 file. Processing can be cancelled.

GZIP uses DEFLATE. Decompression verifies its header, size and CRC-32 and accepts single-member files only. Maximum expanded output is 32 MiB. A CRC check detects accidental corruption; it does not authenticate a file.

About this tool

GZIP compressor compresses a single file locally with fast, balanced, or smallest compression settings and reports the resulting size. It is a quick way to prepare a file for transfer or measure how well it compresses.

The file is compressed in a worker on your device and never uploaded. The output is a standard single-member GZIP file compatible with ordinary command-line tools.

How to use it

  1. Choose the file to compress.
  2. Pick the compression level for the tradeoff you want.
  3. Compare the original and compressed sizes.
  4. Download the .gz file.

Worked example

A 190,117-byte JSON export of 2,000 customer records compresses to:

Fast (level 1):      16,465 bytes   −91.3%
Balanced (level 6):  11,548 bytes   −93.9%
Smallest (level 9):  11,548 bytes   −93.9%

Text with repeated keys and values compresses extremely well. Here the balanced setting already reaches the best result, which is typical: higher levels spend more time for gains that are often tiny.

What compresses and what does not

GZIP (the DEFLATE algorithm) finds repeated sequences of bytes. Text, CSV, JSON, logs, SQL dumps, and SVG often shrink by 70–95%. JPEG, PNG, MP4, ZIP, and PDF files are usually already compressed and may barely shrink, or even grow slightly because of the header.

A .gz file holds exactly one file. To bundle several files, create a ZIP, or on Unix systems a .tar archive that you then gzip (.tar.gz). Web servers use the same algorithm to compress HTML, CSS, and JavaScript on the fly, which is why gzip compression is one of the first web performance checks.

Frequently asked questions

Which level should I choose?

Fast is quickest, balanced is the everyday choice, and smallest spends more time to shave off additional bytes.

Can it compress multiple files into one archive?

No. GZIP wraps a single byte stream; use the ZIP creator to package several files.

What are the limits?

One file up to 16 MiB, 32 MiB combined, with a 60-second processing timeout.

How do I open a .gz file?

Use the GZIP decompressor here, gunzip on macOS and Linux, or 7-Zip on Windows. The decompressed file is byte-for-byte identical to the original.