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RAID Capacity Calculator
Estimate usable capacity for equal-sized drives in RAID 0, 1, 5, 6, or 10. RAID is not a backup.
Result
RAID is not a backup.
RAID 5 usable capacity: 36 TB ≈ 32.74 TiB
≈ 43.66 TiB
≈ 32.74 TiB
TB is decimal manufacturer capacity. TiB is binary (2⁴⁰ bytes) and is not the same unit.
How this was calculated
- Drives are assumed equal in size. Invalid layouts are rejected instead of guessed.
- RAID 0: usable = n × drive size (min 2). RAID 1: 2-drive mirror, usable = one drive.
- RAID 5: usable = (n − 1) × drive size (min 3). RAID 6: usable = (n − 2) × drive size (min 4).
- RAID 10: usable = (n ÷ 2) × drive size, even drive count, min 4.
- Entered TB is decimal (1 TB = 1,000,000,000,000 bytes). Approximate TiB uses 1 TiB = 2⁴⁰ bytes and is not labeled as TB.
Limitations
RAID is not a backup.
- RAID is not a backup. Redundancy is not a second copy you can restore after deletion, ransomware, or a failed array.
- Vendor layouts such as SHR are not implemented here.
- Filesystem overhead, snapshots, and spare drives are not subtracted from usable capacity.
Related guides
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Read guideHow Much NAS Storage Do I Need?
Calculate the NAS capacity you actually need by accounting for your files, growth, RAID or parity, filesystem overhead, snapshots, and free-space headroom. A worked example shows why raw drive capacity is not the same as usable storage.
Read guideRelated glossary
RAID
RAID combines multiple drives to improve capacity, performance, or resilience through striping, mirroring, or parity. It is redundancy, not a backup.
Learn moreRAID 1
RAID 1 mirrors data across two drives, so one drive can fail without immediately making the data unavailable. It reduces usable capacity and is not a substitute for a backup.
Learn moreCMR
CMR (conventional magnetic recording) stores hard-drive tracks without the overlapping layout used by SMR. It can be a useful recording-technology label when comparing drives for write-heavy workloads.
Learn more