RAID Calculator β Usable Capacity & Fault Tolerance
Calculate usable capacity, storage efficiency and fault tolerance for RAID 0, 1, 5, 6 and 10 from your drive count and size.
π Runs entirely in your browser. Your input and output are never sent to a server or stored β fully private.
β RAID protects against drive failure, not against accidental deletion, ransomware or disasters β RAID is not a backup.
About this tool
Planning a NAS, home server or workstation array? Enter the number of drives and their capacity, choose a RAID level β 0, 1, 5, 6 or 10 β and this calculator shows the usable capacity, storage efficiency and how many drive failures the array can survive. It makes the trade-off between space and safety concrete before you buy disks, instead of after. The whole calculation runs locally in your browser, so nothing about your storage setup is uploaded anywhere.
Frequently asked questions
Which RAID level should I choose?
It depends on what you value. RAID 0 stripes for maximum speed and capacity but one failed drive destroys everything. RAID 1 mirrors two drives β simple and safe, but you get half the space. RAID 5 gives good capacity and survives one drive failure; RAID 6 survives two, which matters with today's large disks and their long rebuild times. RAID 10 combines mirroring and striping for performance plus redundancy, at the cost of half the raw capacity.
Does RAID mean my data is backed up?
No β RAID is not a backup, and treating it as one is the most expensive mistake in storage. Redundancy only protects against drive hardware failure. If you delete a file, it is deleted from every drive instantly; ransomware encrypts the whole array at once; a fire, flood, power surge or stolen machine takes all the disks together. Follow the 3-2-1 rule: three copies of your data, on two different media, with one kept off-site.
Why is my usable capacity less than the total of all drives?
Redundancy has to live somewhere. RAID 1 and 10 store a full mirror, so half the raw space goes to copies; RAID 5 reserves one drive's worth for parity and RAID 6 reserves two. On top of that, drives are marketed in decimal gigabytes while operating systems count in binary, so a 4 TB disk shows up as roughly 3.6 TiB. This calculator handles the RAID arithmetic locally in your browser, with nothing sent to any server.