RAID Calculator · Runs in your browser

RAID storage calculator

Enter your drives and RAID level to see usable capacity, how many drives you can lose without losing data, and how efficiently you're using your storage.

Use matching drives; RAID sizes to the smallest one.
usable capacity
raw capacity
drives you can lose
storage efficiency

Reminder: RAID is not a backup. It protects against a drive failing, not against deletion, ransomware, corruption, or fire. Always keep separate backups. See is RAID a backup and the 3-2-1 rule.

What each level does

LevelUsableCan loseGood for
JBOD / RAID 0All drives0 drivesMax space or speed, no safety
RAID 11 drive's worthAll but oneSimple 2-drive mirror
RAID 5All minus 11 driveGood space + one-drive safety (3+ drives)
RAID 6All minus 22 drivesBigger arrays where a rebuild is risky (4+ drives)
RAID 10Half1+ (up to half)Speed + redundancy (4+ even drives)

Note: drive makers count 1 TB = 1,000,000,000,000 bytes, so real formatted capacity is roughly 7% lower than the "TB" on the box. This calculator shows nominal TB.

Where to go next

Picking drives and a NAS? See the best NAS for beginners and whether you need a NAS or a mini PC. Curated drives are on the gear page, and more free tools are in the tools hub.

Related guides