RAID trades raw capacity for redundancy. RAID 5 survives one drive failure; RAID 6 survives two.
How to use the RAID Capacity Calculator
- Number of drives
- Drive size
- RAID level
Results update as you type, and every field accepts the units shown in its menu.
How it works
Usable capacity depends on how many drives’ worth of space is used for parity or mirroring.
Inputs explained
| Field | What to enter |
|---|---|
| Number of drives | A number |
| Drive size | Units: TB, GB |
| RAID level | Choose one: RAID 0 (striping), RAID 1 (mirroring), RAID 5 (single parity), RAID 6 (double parity) … |
Example values
How the main result changes when Number of drives changes and everything else stays at the example values above:
| Number of drives | Usable capacity (TB) |
|---|---|
| 2 | 8 |
| 3 | 16 |
| 4 | 24 |
| 5 | 32 |
| 6 | 40 |
| 8 | 56 |
Formula
RAID 0: n × size; RAID 1: size; RAID 5: (n − 1) × size; RAID 6: (n − 2) × size; RAID 10: n ÷ 2 × sizeWorked example
Inputs — Number of drives: 4; Drive size: 8 TB; RAID level: RAID 5 (single parity).
Results — Usable capacity = 24 TB; Storage efficiency = 75 %; Drive failures tolerated = 1.
Frequently asked questions
Is RAID a backup?
No; it protects against drive failure, not deletion, ransomware or fire.
Why does my OS show less space?
Drives use decimal TB while operating systems often show binary TiB.
What formula does the RAID Capacity Calculator use?
RAID 0: n × size; RAID 1: size; RAID 5: (n − 1) × size; RAID 6: (n − 2) × size; RAID 10: n ÷ 2 × size.