RAID Capacity Calculator
Find out how much usable space your drives give you under each RAID level.
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RAID Capacity Calculator by TheCalcTools
How the RAID Capacity Calculator works
Choose a RAID level, the number of drives and the capacity of each.
RAID 0 stripes with no redundancy, RAID 1 and 10 mirror, and RAID 5 and 6 use one or two drives’ worth of parity.
Usable capacity is the raw capacity minus the redundancy overhead.
The formula
Worked example
Using the default values shown in the calculator:
| RAID level | RAID 5 |
|---|---|
| Number of drives | 6 |
| Drive size (TB) | 4 |
- RAID 5 with six 4 TB drives has 24 TB raw.
- One drive’s worth is used for parity, so usable = 5 × 4 = 20.00 TB.
- Efficiency is 83.3%, and the array tolerates 1 drive failing.
Result:
| Raw capacity (TB) | 24.00 |
|---|---|
| Usable capacity (TB) | 20.00 |
| Storage efficiency | 83.3% |
| Fault tolerance | 1 drive |
Frequently asked questions
Is RAID a backup?
No. RAID protects against drive failure but not against deletion, corruption, ransomware or site loss. Keep separate backups.
Why use RAID 6 on large drives?
Rebuilds on large drives take a long time, and a second failure during a RAID 5 rebuild loses the array. RAID 6 survives two failures.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.