RAID Calculator
Estimate usable storage and fault tolerance.
A RAID calculator works out how much of your raw drive capacity is actually usable under a given RAID level, and how many drives can fail before data is lost. RAID 5 loses one drive's worth to parity, RAID 6 loses two, and RAID 10 halves capacity.
Your input
Private, browser-based processingResults
Ready when you are
Enter your details above and run the tool.
How RAID Calculator works
What it does
Estimate usable storage and fault tolerance.
What you get
Estimated usable capacity, storage overhead and drive-failure tolerance.
On your device
Your input is processed in this browser. Copy or download the result when you are ready.
What if a check cannot finish?
Confirm your input and try again. A timeout, blocked request, or unavailable provider is not proof that a domain is broken. Internet measurements and third-party services have limits.
RAID Calculator — frequently asked questions
Which RAID level should I use?
RAID 6 or RAID 10 for anything you care about. RAID 5 on large modern drives risks a second failure during the long rebuild, and RAID 0 has no redundancy at all.
Is RAID a backup?
No, and this is the mistake that loses data. RAID survives drive failure. It does not survive deletion, ransomware, corruption, theft or fire. Keep separate backups.
Why is usable capacity less than the drives add up to?
Parity and mirroring consume space, and drive vendors count in decimal terabytes while operating systems display binary — roughly 9% smaller on screen.