Estimate usable storage, raw capacity, parity or mirror overhead, reserve overhead, and basic fault tolerance for common RAID layouts.
RAID 0/1/5/6/10
JBOD/no RAID
GB, TB, GiB, TiB
Estimate-only storage math
Capacity result
Estimated usable storage
RAID 5 estimated usable capacity0 TB
Enter drive details to estimate capacity.
Raw drive capacity
0 TB
Usable before reserve
0 TB
Usable after reserve
0 TB
RAID parity or mirror overhead
0 TB
Reserved overhead
0 TB
Fault tolerance
1 drive
Minimum drives
3 drives
Layout note
Estimate only.
RAID is not backup. Keep separate backups for important data.
How the RAID capacity calculator works
The calculator multiplies drive count by drive size to estimate raw capacity, then applies the selected RAID layout. RAID 0 and JBOD use all entered capacity, RAID 1 mirrors data, RAID 5 reserves one drive worth of parity, RAID 6 reserves two drives worth of parity, and RAID 10 uses mirrored pairs.
The optional reserved overhead field subtracts an additional planning cushion for filesystem metadata, snapshots, hot spare policy, free-space targets, or practical headroom.
Same-size drive assumption
This first version assumes every drive has the same usable size. If you mix drive sizes in standard RAID, capacity is often limited by the smallest drive. For a conservative estimate, enter the smallest drive size.
Some NAS platforms offer vendor-specific mixed-drive layouts that can use more capacity than traditional RAID. Treat this page as a planning estimate before checking your vendor's final storage pool calculator.
What each RAID level means
RAID 0 stripes data and gives high capacity, but one failed drive can break the array. RAID 1 mirrors data and is simple, but capacity is limited to one drive in a same-size mirror. RAID 5 and RAID 6 use parity to recover from one or two failed drives. RAID 10 mirrors pairs and stripes across those pairs.
Fault tolerance does not protect against accidental deletion, malware, fire, theft, controller problems, bad updates, or multiple failures outside the layout's limits. Use RAID for availability, not as your only copy of important files.
RAID capacity FAQ
Why does my NAS show less space? The NAS may use binary units, metadata, snapshots, filesystem reserves, hot spares, or a vendor-specific storage layout.
Should I use TB or TiB? Use TB for decimal drive labels and TiB when comparing against operating-system or NAS screens that report binary capacity.
