RAID Capacity Calculator
Work out usable capacity, redundancy and storage efficiency for RAID 0, 1, 5, 6 and 10 from your disk count and disk size. Calculates in your browser.
Usable capacity
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Show the math
Usable capacity depends on how each level spends disks on redundancy:
0: n·s · 1: s · 5: (n−1)·s · 6: (n−2)·s · 10: (n÷2)·s
n is the disk count and s the size of one disk. RAID 5 sacrifices one disk to parity, RAID 6 two, and RAID 10 mirrors so half the raw capacity is usable. Assumes equal-sized disks; mixed sizes are limited by the smallest. Calculated entirely in your browser.
What this does
A RAID calculator works out usable capacity, redundancy and storage efficiency for RAID 0, 1, 5, 6 and 10.
How to use it
- Enter the number of disks.
- Enter each disk’s size.
- Pick the RAID level.
- Read usable capacity and fault tolerance.
How it works
RAID 0 uses every disk, RAID 1 mirrors down to one, RAID 5 loses one disk to parity, RAID 6 loses two, and RAID 10 gives half the raw capacity. Disks are treated as the size of the smallest.
Understanding your result
Usable capacity is what you can store; the redundancy is what keeps the array alive when a disk dies, and the two trade off. RAID is not a backup, it survives a disk failure, not a deletion, fire, or ransomware, so keep separate backups. All disks are sized to the smallest, so mixing a large disk in wastes its extra space.
Example
Four 4 TB disks in RAID 5 give 12 TB usable and tolerate one disk failure.
Sources & methodology
Last updated .
Frequently asked questions
How is usable RAID capacity calculated?
It depends on the level: RAID 0 uses every disk, RAID 1 mirrors down to one disk, RAID 5 loses one disk to parity, RAID 6 loses two, and RAID 10 gives you half the raw capacity.
What does fault tolerance mean here?
It is how many disks can fail without losing data. RAID 0 tolerates none, RAID 5 one, RAID 6 two, and RAID 10 at least one (and often more, depending on which disks fail).
Does it assume equal disk sizes?
Yes. In most arrays every disk is treated as the size of the smallest, so the calculator uses one capacity for all disks.
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