RAID Calculator

Work out how much usable space a RAID array gives you. Pick a RAID level, the number of disks and the size of each disk, and the calculator shows usable capacity, storage efficiency, how many disk failures the array survives and a rough read/write speed factor. Free and instant in your browser.

This RAID calculator works out usable storage capacity for RAID 0, 1, 5, 6, 10, 50 and 60 from the number of disks and the size of each one. It shows how much space you actually get, the storage efficiency as a percentage, how many drive failures the array can survive, and a rough read and write speed factor. Admins use it to compare RAID levels before buying drives, to size a NAS or server, and to answer questions like how much usable space RAID 5 gives or how many disks you can lose. The math is standard and runs instantly in your browser.

Read the guide: How to Calculate RAID Capacity
Usable capacity
12 TB
75.0% of 16 TB raw · survives 1 disk failure
Usable capacity
12 TB
Raw capacity
16 TB
Storage efficiency
75.0%
Fault tolerance
1 disk
Read speed factor
3×
Write speed factor
1×

How it works

  1. 1

    Pick a RAID level

    Choose from RAID 0, 1, 5, 6, 10, 50 or 60. Each balances capacity, redundancy and speed differently.

  2. 2

    Enter your disks

    Set the number of disks and the size of each one, in GB or TB. The disks are assumed to be the same size.

  3. 3

    Read the result

    See usable capacity, efficiency as a percentage, the number of disk failures tolerated, and read and write speed factors.

Instant & 100% private — nothing is uploaded

Everything runs locally in your browser. Your code, text and files are processed on your own device and are never sent to a server — so there are no upload waits, no size limits from us, and nothing is ever stored or logged.

Frequently asked questions

How is usable RAID capacity calculated?
It depends on the level. RAID 0 gives all of it. RAID 1 gives one disk worth. RAID 5 loses one disk to parity, so usable is (disks − 1) × size. RAID 6 loses two. RAID 10 gives half, since every disk is mirrored. RAID 50 and 60 split the disks into groups and apply RAID 5 or 6 parity within each group, so they lose one or two disks per group.
How many disk failures can each RAID level survive?
RAID 0 survives none, a single failure loses the array. RAID 1 survives every disk but one. RAID 5 survives one failure, RAID 6 survives two. RAID 10 survives at least one, and more if the failures fall in different mirror pairs. RAID 50 survives one per group and RAID 60 two per group.
What do the read and write speed factors mean?
They are a rough multiplier against a single disk, based on how many disks the data is striped across. A higher read factor means faster reads; parity levels write more slowly because parity has to be computed and written. They are a guide for comparing layouts, not a benchmark of any specific controller.

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