RAID Capacity
Estimate usable capacity for a RAID disk set.
RAID Capacity Calculator
Calculate approximate usable capacity for RAID 0, 1, 5, 6 or 10.
IT Calculators
Quickly estimate transfer time, RAID capacity, backup storage, SLA downtime and more.
How to use RAID Capacity Calculator
Calculate approximate usable capacity for RAID 0, 1, 5, 6 or 10.
What this tool is for
A calculator provides an estimate from the values you enter. The result becomes useful when units, assumptions and margins are explicit.
Recommended workflow
- Enter realistic values and carefully check the units.
- Run the calculation and record both the result and the assumptions used.
- Run a second conservative scenario to measure the margin before making a decision.
Best practices
- Always distinguish decimal and binary units when storage is involved.
- Allow margin for protocol overhead, throughput variation and operational uncertainty.
- Use the result as a sizing estimate, not as a contractual guarantee.
Questions about this tool
Why is usable RAID capacity lower than raw disk capacity?
Parity, mirroring and the number of disks reserved by the RAID level reduce usable capacity. Filesystem and vendor units can reduce the displayed value further.
Can I mix disks of different sizes?
Usually the smallest participating disk limits the effective size per member, so mixed sizes can waste capacity and complicate replacement planning.
Does RAID replace backups?
No. RAID improves availability against some disk failures; it does not protect against deletion, corruption, ransomware or site loss.