RAID Storage Capacity Calculator
Estimate usable storage capacity and redundancy for common RAID levels (0, 1, 5, 6, 10) from disk size and count.
Your results
Calculation breakdown
- RAID 0
- usable = disks × size (no redundancy)
- RAID 5
- usable = (disks − 1) × size
- RAID 6
- usable = (disks − 2) × size
- RAID 10
- usable = (disks ÷ 2) × size
Worked example
Four 4 TB disks in RAID 5 give (4 − 1) × 4 TB = 12 TB usable capacity, tolerating one disk failure.
Assumptions
- Assumes all disks are the same size; mixed sizes reduce usable capacity to the smallest disk's size.
- RAID is not a substitute for a separate backup.
How this calculator works
Enter the number of disks and the size of each disk to estimate usable capacity under RAID 0, 1, 5, 6 or 10, plus how many disk failures each level can tolerate. Useful for sizing a home NAS.
Frequently asked questions
Which RAID level gives the most usable space?
RAID 0 gives the most usable space (100% of raw capacity) but offers no redundancy — a single disk failure loses all data.
What is RAID 5 good for?
RAID 5 balances capacity and protection, tolerating one disk failure while using only one disk's worth of capacity for parity.
Is RAID a backup?
No, RAID protects against a disk failure but not against accidental deletion, ransomware or theft — a separate backup is still needed.