THE NUMBERS, EXPLAINED
How to use this calculator.
Equal-capacity drives assumed. Formatting, spares and filesystem reserves are excluded. RAID is not a backup.
Start with your inputs
Enter drive count, drive size (tb), raid level (0,1,5,6,10). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Drive count | 4 |
| Drive size (TB) | 4 |
| RAID level (0,1,5,6,10) | 5 |
A worked example
With the example inputs above, nominal usable tb is 12. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Nominal usable TB | 12 |
How this is calculated
Nominal usable TB
RAIDcapacity(a,b,c)
Symbols and units
- a
- Drive count
- b
- Drive size (TB)
- c
- RAID level (0,1,5,6,10)
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Calculation steps and notation
For n equal drives of size S: RAID 0 capacity = nS; RAID 1 = S; RAID 5 = (n−1)S; RAID 6 = (n−2)S; RAID 10 = nS/2. Minimum drive counts and the even drive count for RAID 10 are checked.
Assumptions and limits
Equal-capacity drives assumed. Formatting, spares and filesystem reserves are excluded. RAID is not a backup.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Nominal usable TB. The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Equal-capacity drives assumed. Formatting, spares and filesystem reserves are excluded. RAID is not a backup.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
Read the quality report →