Compression
What does a 4:1 compression ratio mean?
75% smaller
4:1 means the compressed file is ¼ of the original: 100 MB becomes 25 MB.
A ratio compares the original size to the compressed size. 4:1 means the compressed file is a quarter of the original, which is a 75 % saving. People mix up ratios and percentages often.
The arithmetic
- ratio = original ÷ compressed = 100 MB ÷ 25 MB = 4:1
- saving = 1 − 1 ÷ ratio = 1 − ¼ = 75 %
- Doubling the ratio never doubles the saving: 2:1 saves 50 %, 4:1 saves 75 %, 8:1 saves 87.5 %
| Ratio | Size left | Space saved |
|---|---|---|
| 1.1:1 | 90.9 % | 9.1 % |
| 1.25:1 | 80 % | 20 % |
| 1.5:1 | 66.7 % | 33.3 % |
| 2:1 | 50 % | 50 % |
| 3:1 | 33.3 % | 66.7 % |
| 4:1 | 25 % | 75 % |
| 5:1 | 20 % | 80 % |
| 10:1 | 10 % | 90 % |
| 20:1 | 5 % | 95 % |