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RAID Calculator

Find usable storage capacity for a RAID array from disk count, disk size and RAID level.

Inputs

Saved Scenarios

— select 2+ to compare

Usable Capacity (TB)

16.00

Raw Capacity (TB)

20.00

Spark says

How it's calculated

Formula

RAID 5:(N−1)×SRAID 6:(N−2)×SRAID 10:N2×SRAID\ 5: (N-1) \times S \quad RAID\ 6: (N-2) \times S \quad RAID\ 10: \dfrac{N}{2} \times S
N
— Number of disks
S
— Size of each disk

What is the RAID Calculator?

Different RAID levels trade off usable capacity against redundancy and performance — this calculator applies the standard capacity formula for each level to a given disk count and size.

How to use it

  1. 1 Choose a RAID level.
  2. 2 Enter the number of disks.
  3. 3 Enter the size of each disk (assumes identical disks, which RAID requires anyway).

Worked examples

5 × 4TB disks, RAID 5

16TB usable out of 20TB raw.

Try it

Limitations

  • •RAID 5 needs at least 3 disks and RAID 6 needs at least 4 to make physical sense — with fewer disks than that, this calculator's formula will show a result but the RAID level itself isn't actually viable; check your controller's minimum requirements.

Frequently asked questions

Why does RAID 1 usable capacity not increase with more disks?

RAID 1 mirrors the same data across every disk in the array — adding more mirror disks increases redundancy, not capacity, so usable space always equals one disk's size.