Compression Ratio Calculator
Compression ratio, space saved and the throughput trade — including whether compressing before sending actually makes a transfer faster.
The ratio is original over compressed; the saving is the complement.
How the compression ratio calculator works
The ratio is original over compressed; the saving is the complement. A 4:1 ratio saves 75%, and the gap between "4:1" and "75%" is where most confusion lives — a 2:1 ratio saves half, but 10:1 saves 90%, not five times as much.
The interesting question is whether compressing pays on a transfer. It does when the time to compress plus the time to send the smaller file beats sending the original — which depends entirely on the link speed. On a fast link, compression can make a transfer slower.
Formula: ratio = original / compressed; saving = 1 − 1/ratio
Worked examples
| Inputs | Compression ratio | Note |
|---|---|---|
| 850 MB down to 190 MB | 4.474 | 4.47:1, 78% saved |
| A fast link | 4.474 | compressing costs more than it saves |
| Barely compressible | 1.063 | 1.06:1 |
FAQFrequently asked questions
What is a good compression ratio?
Text and logs commonly reach 5:1 to 10:1. Already-compressed data — video, images, archives — reaches about 1:1, because the redundancy is gone.
Is 4:1 the same as 75% saved?
Yes. Ratio and percentage saved are the same fact stated two ways, and the relationship is not linear — 10:1 is 90%, not 250%.
Can compressing make a transfer slower?
Yes. On a fast link the time spent compressing exceeds the time saved sending fewer bytes. The break-even row shows where that flips.
Why does already-compressed data not compress?
Because compression removes redundancy, and there is none left. Recompressing a JPEG or a zip gains nothing and often adds a few bytes.
What about compression level?
Higher levels give a better ratio at sharply diminishing returns and much slower throughput. The middle levels are usually the right trade.
Where these figures come from
- IEC 80000-13 — Information science and technology (quantities and units) — the decimal (kB, MB) versus binary (KiB, MiB) prefixes used throughout
- RFC 4632 — Classless Inter-domain Routing (CIDR) — the address-plan arithmetic behind the subnet calculator
- RFC 1918 — Address Allocation for Private Internets — the private ranges the subnet calculator recognises
- NIST SP 800-63B — Digital Identity Guidelines, Authentication — length over composition rules; the basis of the password guidance here
- NIST SP 800-57 Part 1 — Recommendation for Key Management — key-strength comparisons used by the key-space calculator
- NIST — Digital Identity Guidelines (SP 800-63) — US federal authentication standard
Last checked: September 2026. Units follow the SI decimal convention (IEC 80000-13 defines the binary alternatives); network and security figures cite the defining standard.