Calculate compression ratio and space saved between an original and compressed file size, in either direction, and sanity-check your result against typical real-world ratios for ZIP, video, images, and audio.
| Type | Typical Ratio | Space Saved |
|---|
Enter your details and click Calculate to see results
Compression ratio is the standard way to express how much a compression algorithm shrank a file, and this compression ratio calculator computes it directly from an original and a compressed file size — whichever two numbers you have, in either direction. It's useful whether you're comparing archive tools, evaluating a new video codec, checking whether a backup job is actually compressing your data, or just curious how much smaller a ZIP or gzip made a folder of files.
It converts your original and compressed sizes to a common unit and computes compression ratio = original ÷ compressed, expressed as X:1, along with space saved as both a percentage and an absolute amount.
Backend engineers evaluating a backup or logging compression strategy, developers comparing archive tools or video codecs, DBAs checking whether a database dump compresses as expected, and anyone curious how much smaller a ZIP or gzip made their files need this original-vs-compressed comparison.
A compression ratio in isolation doesn't tell you much without context — 2:1 is excellent for already-compressed video but disappointing for plain text, which typically compresses 3:1 or better with gzip. Comparing your actual result against typical real-world ratios helps you judge whether an encoder setting, backup tool, or storage format is performing as expected, or whether something (like re-compressing already-compressed data) is limiting your results.
How this calculator turns two file sizes into a ratio and percentage
Ratio and percentage always correspond exactly: a 4:1 ratio is always 75% saved, a 10:1 ratio is always 90% saved — they're two ways of expressing the same relationship.
ZIP and similar archivers achieve roughly 2:1 on typical mixed files. Gzip on plain text can do better, often 3:1 or higher.
Video, image, and audio codecs use specialized, lossy techniques. H.265 roughly halves H.264's bitrate (~2:1), JPEG can be 5-10× smaller than PNG for photos.
A compression ratio of 4:1 means the original is four times the compressed size — equivalent to 75% space saved.
From entering two sizes to reading your ratio and space saved
Type the uncompressed (original) file or folder size into the Original Size field.
Select KB, MB, or GB so the value matches how your file manager or backup tool reports it.
Type the size of the file after compression (e.g., the resulting .zip, .gz, or encoded output).
Select the matching unit — the calculator converts both sizes to a common unit automatically.
See the compression ratio, percentage and absolute space saved, and how your result compares to typical real-world ratios.
Using the calculator's own default scenario — 500 MB original, 125 MB compressed
Suppose your original file is 500 MB and the compressed version is 125 MB.
Explanation: A 4:1 ratio (75% space saved) is a strong result, typical of text-heavy or structured data compressed with gzip or ZIP at a good compression level. If this were a video or JPEG file instead, a 4:1 ratio would be unusually high — media files already compressed with a specialized codec typically see ratios much closer to 1:1 under general-purpose compression.
What your ratio generally implies about the data and algorithm
| Ratio | What It Generally Means | Recommended Next Step |
|---|---|---|
| Under 1.1:1 | Little to no compressible redundancy | Likely already-compressed or encrypted data — expected, not a problem |
| 1.1:1 – 2:1 | Modest compression, typical of mixed/media files | Normal for images, video, and general binary data |
| 2:1 – 5:1 | Solid compression, typical of structured/text data | Expected range for logs, JSON, CSV, and general ZIP archives |
| Over 5:1 | Excellent compression, highly repetitive data | Common for verbose logs or SQL dumps; verify data integrity after decompression |
If your ratio is much lower than expected: check whether the source data is already compressed or encrypted, or whether your tool's compression level is set to "fastest" rather than "maximum."
If your ratio is unexpectedly high: that's usually good news for repetitive text data, but double-check the decompressed output matches the original if using a lossless format.
Reference ratios are typical industry figures — actual results vary with content type, encoder settings, and file structure.
This calculator compares file sizes only. It does not evaluate compression speed, CPU cost, or — for lossy formats — perceptual quality loss.
Where comparing original vs compressed size genuinely helps
Check whether a backup job's compression ratio is reasonable for the data type.
Compare gzip vs zstd vs brotli ratios on application log samples.
Run the same file through multiple tools and compare resulting ratios.
Estimate compressed backup storage needs from an expected compression ratio.
Compare H.264 vs H.265 file sizes at matching quality settings.
Compare JPEG vs PNG vs WebP compression ratios for a photo library.
Compare FLAC vs MP3 vs WAV size tradeoffs for a music library.
Quantify storage savings from compressing data before uploading to object storage.
Verify a newly configured compression pipeline performs as expected.
Generate concrete percentage-saved figures for a storage optimization report.
Use it in a course to make ratio vs percentage-saved concrete for students.
Verify a compression-level change actually improved your ratio meaningfully.
What this compression ratio calculator does well, and where it can't replace real testing
Industry-typical ratios for common compression scenarios
| Format / Scenario | Typical Ratio | Space Saved |
|---|---|---|
| ZIP (general mixed files) | ~2:1 | ~50% |
| Gzip (plain text) | ~3:1 or better | ~67%+ |
| SQL dump (gzip) | 4:1 – 10:1 | 75% – 90% |
| H.265 vs H.264 (same quality) | ~2:1 | ~50% |
| JPEG vs PNG (photos) | 5:1 – 10:1 | 80% – 90% |
| FLAC vs WAV (audio) | ~2:1 | ~50% |
| Already-compressed media re-zipped | ~1:1 | ~0% |
Summary: This compression ratio calculator gives you an instant, free way to compute compression ratio and space saved between any two file sizes, with a reference table to sanity-check your result against typical industry figures. Pair it with the File Size Calculator and Storage Converter for a complete file-size toolkit.
Common questions about compression ratio calculator results
Official standards documentation to complement this calculator
Explore other tech tools