RAID Capacity Calculator

Plan equal-disk RAID 0, 1, 5, 6, or 10 arrays with transparent capacity formulas and resilience limits.

Array configuration

Model equal-size drives in a common RAID layout.

RAID level

Number of disks

Size of each disk

Manufacturer unit

Usable capacity

12 TB

Raw capacity

16 TB

Parity / mirror overhead

4 TB

Storage efficiency

75%

Approximate TiB

10.914 TiB

Fault-tolerance model

1 disk failure

Capacity and resilience limits

All disks are assumed equal; mixed arrays are normally limited by the smallest disk. Filesystem, metadata, controller, spare, and reserved-space overhead are not deducted.

RAID improves availability but is not backup. It does not protect against deletion, corruption, theft, malware, controller failure, fire, or multiple failures beyond the layout's tolerance.

Capacity by RAID level

RAID 0 uses every disk for data but has no redundancy. RAID 1 mirrors the same data. RAID 5 and RAID 6 reserve the equivalent of one and two disks for distributed parity. RAID 10 mirrors pairs and stripes across them.

The calculator uses manufacturer decimal GB or TB for input and also shows the approximate binary GiB or TiB operating systems may display.

Availability is not backup

RAID can keep a system available after specific disk failures, but it cannot recover deleted or corrupted files and does not replace independent, tested backups.

Formula variables

$n$: Number of equal-size disks
$S$: Capacity of the smallest disk

RAID 0

C=nS

RAID 1

C=S

RAID 5

C=(n-1)S

RAID 6

C=(n-2)S

RAID 10

C=\frac{n}{2}S

Examples

Four-disk RAID 5

Input

4 × 4 TB drives

Show result

Result

12 TB usable, 4 TB parity overhead, 75% efficiency

Frequently Asked Questions

Can I mix drive sizes?

Many arrays can, but each disk is generally treated as no larger than the smallest member for capacity planning.

Is RAID a backup?

No. Keep separate, versioned, tested backups.

References

SNIA Dictionary — RAID

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