Calculate deduplication ratio, percentage saved, and stored size from original and deduplicated data sizes, or convert ratio and % both ways.
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Deduplication Ratio To Percentage Formula
The calculator uses one of three formulas depending on which mode you select.
From data sizes:
Ratio to percentage:
Percentage to ratio:
- Original: data size before deduplication, in any decimal unit (B, KB, MB, GB, TB, PB); each prefix step multiplies bytes by 1,000.
- Stored: actual size on disk after deduplication, in the same or any other unit.
- Ratio: deduplication ratio expressed as x:1.
- % Saved: storage capacity reduction as a percentage.
The "From data sizes" mode takes raw before and after sizes and outputs both the ratio and the percentage saved. "Ratio to %" converts a known x:1 ratio into the matching reduction percentage. "% to ratio" goes the other direction, turning a reported savings percentage into an x:1 ratio.
Reference Tables
Use the table below to convert between common deduplication ratios and the percentage of storage saved.
| Ratio | % Saved | Stored Fraction |
|---|---|---|
| 1.5:1 | 33.33% | 66.67% |
| 2:1 | 50.00% | 50.00% |
| 3:1 | 66.67% | 33.33% |
| 4:1 | 75.00% | 25.00% |
| 5:1 | 80.00% | 20.00% |
| 10:1 | 90.00% | 10.00% |
| 20:1 | 95.00% | 5.00% |
| 50:1 | 98.00% | 2.00% |
| 100:1 | 99.00% | 1.00% |
Illustrative ratio ranges for arithmetic examples, not validated workload expectations. Actual reduction depends on the dataset and storage product:
| Example context | Illustrative Ratio | Approx. % Saved |
|---|---|---|
| VDI / virtual desktops | 10:1 to 20:1 | 90% to 95% |
| Backup data | 10:1 to 30:1 | 90% to 97% |
| VM file systems | 3:1 to 8:1 | 67% to 88% |
| General file shares | 1.5:1 to 3:1 | 33% to 67% |
| Databases (active) | 1.2:1 to 2:1 | 17% to 50% |
| Encrypted or compressed media | ~1:1 | 0% to 5% |
Examples and FAQ
Example 1. You started with 100 GB of data and the array reports 25 GB stored. Ratio = 100 / 25 = 4:1. Percent saved = (1 - 25/100) * 100 = 75%. You saved 75 GB of capacity.
Example 2. A vendor reports a 10:1 deduplication ratio. Percent saved = (1 - 1/10) * 100 = 90%. For every 1 TB ingested, only 100 GB is actually stored.
Is a higher ratio always better? A higher ratio means more savings, but the gain per step shrinks. Going from 2:1 to 4:1 increases savings from 50% to 75%, a 25-percentage-point increase. Going from 10:1 to 20:1 only moves savings from 90% to 95%.
Does deduplication include compression? Sometimes. Some vendors report a combined data reduction ratio that includes both deduplication and compression. Check whether the number is dedupe-only or total reduction before comparing systems.
Why is my ratio close to 1:1? The data has little repetition. Pre-compressed files, encrypted volumes, and unique media files do not deduplicate well because the byte patterns rarely repeat.
Can the percentage saved be negative? Yes, if the stored size exceeds the original size due to metadata overhead on data that cannot be reduced. The calculator flags this case.
