Calculate backup capacity from total data size, redundancy factor, and compression ratio, or solve any missing value in KB, MB, GB, or TB.
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Backup Capacity Formula
The calculator uses total data size, redundancy factor, and compression ratio to calculate backup capacity. All storage values are converted to gigabytes internally, then converted back to the unit you selected.
BC = (DS * RF) / (1 - CR)
- BC = backup capacity
- DS = total data size
- RF = redundancy factor as a decimal
- CR = compression ratio as a decimal
If backup capacity is the missing value, the calculator uses the formula above. If another value is missing, it rearranges the same formula:
DS = (BC * (1 - CR)) / RF
RF = (BC * (1 - CR)) / DS
CR = 1 - (DS * RF) / BC
The calculator has four functions:
- Calculate backup capacity: enter data size, redundancy factor, and compression ratio.
- Calculate total data size: enter backup capacity, redundancy factor, and compression ratio.
- Calculate redundancy factor: enter data size, backup capacity, and compression ratio.
- Calculate compression ratio: enter data size, redundancy factor, and backup capacity.
Common Backup Planning Values
Use these ranges as general reference values when choosing inputs.
| Input | Typical value | Meaning |
|---|---|---|
| Redundancy factor | 1.0 | One full copy of the data. |
| Redundancy factor | 2.0 | Two full copies, such as a primary backup and a secondary backup. |
| Compression ratio | 0.10 to 0.50 | Decimal input used in the formula as 1 – CR. |
| Unit | Calculator conversion |
|---|---|
| 1 KB | 0.000001 GB |
| 1 MB | 0.001 GB |
| 1 GB | 1 GB |
| 1 TB | 1,000 GB |
Example Calculations
Example 1: Calculate backup capacity
You have 500 GB of data, a redundancy factor of 1.5, and a compression ratio of 0.25.
BC = (500 * 1.5) / (1 - 0.25)
BC = 750 / 0.75 = 1000 GB
The required backup capacity is 1,000 GB, or 1 TB.
Example 2: Calculate compression ratio
You have 2 TB of data, a redundancy factor of 1.2, and 3 TB of backup capacity.
CR = 1 - (2 * 1.2) / 3
CR = 1 - 2.4 / 3 = 0.2
The compression ratio is 0.20.
FAQ
What does redundancy factor mean?
Redundancy factor represents how many effective copies of the data you need to store. A value of 1 means one full copy. A value of 2 means enough capacity for two full copies. Values between those numbers can represent partial redundancy, retention overhead, or other backup policy requirements.
Why do I need to enter exactly three values?
There are four variables in the formula: total data size, redundancy factor, compression ratio, and backup capacity. The calculator needs three known values to solve for the fourth. If you enter fewer or more than three, the missing value cannot be identified correctly.
Which storage unit should I use?
You can use KB, MB, GB, or TB. The calculator converts the selected unit to GB for the calculation and then converts the result back to your selected output unit. It uses decimal conversions, where 1 TB equals 1,000 GB.
