Compression Ratio Calculator
Calculate the compression ratio between an original and compressed file size — with space saved, percentage saved, decimal ratio and a compression-quality rating.
Input
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
What is a compression ratio?
The compression ratio compares a file's original (uncompressed) size to its compressed size. It's the single number most often used to judge how effective a compression algorithm or codec setting was: ratio = original size / compressed size. A ratio of 4:1 means the compressed file is a quarter of the original size; a ratio below 1:1 means the "compressed" output actually grew, which can happen with already-compressed formats (JPEG, MP4, ZIP-of-ZIPs) or very small files where container overhead dominates.
This calculator takes your original and compressed sizes — each with its own unit (bytes through terabytes) — and reports the ratio as both a familiar X:1 figure and a precise decimal, alongside the space saved, the percentage saved, the percentage remaining, and a plain-language quality rating (Low, Moderate, Good, Excellent, Extreme, or Negative if the file grew).
Why it matters
Compression ratio is a quick proxy for algorithm efficiency and storage/bandwidth savings. Backup and archival tools (tar+gzip, zstd, 7-Zip) are often compared by the ratios they achieve on the same dataset — a higher ratio at similar speed usually means lower storage cost and faster transfers. For lossy formats (images, audio, video), a higher ratio isn't automatically "better" — it trades away quality, so ratio is only half the picture. For lossless formats (text, logs, source code, most archives), a higher ratio is close to a pure win, limited mainly by how repetitive the data is: plain text and logs compress far better than already-dense or high-entropy data (video, encrypted files, random binaries).
How to use it
- Enter the Original Size and pick its unit (B, KB, MB, GB, or TB).
- Enter the Compressed Size and pick its unit — the two sizes don't need matching units; mix KB and GB freely.
- Results update automatically: the compression ratio (e.g.
4:1), the decimal ratio, the space saved, percentage saved, percentage remaining, and a quality rating. - Copy the ratio directly, or copy/download the full breakdown table as CSV for a report or spreadsheet.
FAQ
What's a "good" compression ratio? It depends entirely on the data type. Highly compressible data (plain text, logs) commonly reaches 5:1 to 10:1 or higher with general-purpose compressors. Already-compressed or high-entropy data (JPEG, MP4, encrypted files) often lands near 1:1, since there's little redundancy left to remove.
Why is my ratio less than 1:1? The "compressed" file is larger than the original. This happens when compressing data that's already compressed or encrypted (no redundancy to exploit) or when a compression format's container/header overhead outweighs the savings on a very small file.
Does this tool actually compress my files? No — it only calculates the ratio from sizes you provide. Check a real file's size before and after compressing it with your tool of choice (zip, gzip, zstd, etc.) and enter both values here.
What does "space saved" mean? The absolute difference between the two sizes (original minus compressed), shown in the most readable unit — e.g. "7.5 MB saved" rather than a raw byte count.
Privacy
All calculations run entirely in your browser. The sizes you enter are never uploaded or stored — nothing leaves your device.