How to Calculate Data Compression Ratio
What is Data Compression Ratio?
A data compression ratio calculator measures how effectively a compression algorithm reduces file size. A ratio of 3:1 means the compressed file is one-third the size of the original.
Formula
ratio = original_size / compressed_size; savings % = (1 - compressed/original) × 100
- S_orig
- Original size (bytes) — Uncompressed file size
- S_comp
- Compressed size (bytes) — Compressed file size
- ratio
- Compression ratio ((dimensionless)) — How many times smaller the compressed file is
Step-by-Step Guide
- 1Compression Ratio = Original Size ÷ Compressed Size
- 2Space Saving % = (1 − 1/Ratio) × 100
- 3Lossless: exact original recoverable (ZIP, PNG, FLAC)
- 4Lossy: some data discarded for higher ratios (JPEG, MP3)
Worked Examples
Input
100MB → 35MB compressed
Result
Ratio 2.86:1, saving 65%
Input
1GB video → 250MB
Result
Ratio 4:1, saving 75%
Input
ZIP typical text file
Result
Ratio 2:1 to 5:1 typical
Frequently Asked Questions
What is a good compression ratio?
Depends on file type. Text: 3–10× (highly compressible). Images (PNG, JPG): 1.5–3× (already compressed). Video: 10–100×.
Which compressor should I use?
Text/code: gzip, brotli, or zstd. Archives: ZIP, RAR, 7z. Images: WebP, HEIC (lossy). Video: H.264, H.265, AV1 (lossy).
What is lossy vs lossless compression?
Lossless: no data loss; compresses less (text, code, data). Lossy: accepts small quality loss; compresses more (images, audio, video).
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