RAID Calculator

Calculate usable disk capacity for RAID 0, 1, 5, 6 and 10. Enter the number of drives, size per drive and RAID level.

Capacity breakdown
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Raw capacity
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Usable capacity
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Lost to redundancy
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Efficiency
Usable Redundancy

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Frequently asked questions

What RAID level should I use?
RAID 0 for speed with no redundancy. RAID 1 for simple mirroring (2 drives). RAID 5 for a balance of speed and redundancy (minimum 3 drives). RAID 6 for higher fault tolerance (minimum 4 drives). RAID 10 for speed and redundancy (minimum 4 drives, must be even).
Why is usable capacity less than total drive capacity?
RAID uses one or more drives (or equivalent space) for parity or mirroring. For example, RAID 5 with 4 x 1 TB drives gives ~3 TB usable because one drive's worth is used for parity.
Does this account for filesystem overhead?
No. This calculates raw usable capacity. Actual formatted capacity will be slightly less due to filesystem overhead (NTFS, ext4, ZFS, etc.).