RAID usable capacity calculator
Pick a RAID level and your drives to see real usable capacity, what you lose to redundancy, and how many drives can fail before you lose data.
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Usable capacity
48 TB
≈ 43.7 TiB as your OS reports it
- Raw capacity
- 64 TB
- Lost to redundancy
- 16 TB · 75% usable
- Drive failures survived
- 1 drive
How redundancy costs capacity. RAID 5 reserves one drive's worth of space for parity; RAID 6 reserves two; RAID 10 mirrors everything, so half your raw capacity is the cost of protection. RAID 0 and JBOD keep all of it but survive zero failures.
Usable TB uses the drive's labeled (decimal) capacity. Your OS counts in binary, so a 16 TB drive shows as ~14.5 TiB — the TiB figure above reflects that. Always leave headroom; a pool above ~80% full slows down and complicates expansion.