How to use it
- Enter the original size and the compressed size.
- Pick the unit both sizes are in; it only affects how the saved space is shown.
- Read the ratio, the savings and the bits per byte.
Formulas
- Compression ratio = original ÷ compressed (written as x:1)
- Space savings = (1 − compressed ÷ original) × 100 %
- Compressed share = compressed ÷ original × 100 %
- Space saved = original − compressed
- Bits per byte = 8 × compressed ÷ original
Worked example
A 1,000 KB log file compresses to 320 KB:
- ratio: 1000 ÷ 320 = 3.125 : 1;
- savings: 1 − 320 ÷ 1000 = 68 %, so the file is 32 % of its original size;
- space saved: 680 KB;
- bits per byte: 8 × 0.32 = 2.56.
Tips
- Text compresses well, media does not. Logs, CSV and JSON often shrink 4–10 times; photos, video and archives barely shrink again.
- Compare like with like. Measure all compressors on the same input and at the same level; a higher level gives a better ratio but takes more time.
- To see how long the compressed file takes to transfer, use the download time calculator.