RAID Calculator
Related tools
Capacity breakdown
- Usable: 12 TB (75%)
- Redundancy: 4 TB (25%)
| Usable capacity | 12 TB |
|---|---|
| Real usable (formatted) | 10.91 TiB |
| Raw capacity | 16 TB |
| Fault tolerance | 1 disks |
| Storage efficiency | 75% |
| Active disks | 4 |
| Hot spares | 0 |
Real usable is the advertised capacity shown in binary units (TiB) after formatting — the same bytes, about 9% smaller than the decimal figure drives are sold in.
Related reading
- Picking a RAID Level: Capacity, Redundancy, and the Math Behind ItCompare RAID 0, 1, 5, 6, and 10 by usable capacity, fault tolerance, and efficiency, with the formulas and a worked example, so you can size an array with confidence.
- How Long Will That Transfer Really Take? Bits, Bytes, and BandwidthWhy "1 Gbps, 100 GB, 100 seconds" is wrong, and how to read a transfer-time estimate correctly using bits vs bytes and the gap between bandwidth, throughput, and goodput.
- Subnetting Without the Binary Headaches: A Practical CIDR GuideUnderstand CIDR prefixes, subnet and wildcard masks, network and broadcast addresses, and usable host ranges for IPv4 and IPv6, without doing the binary by hand.
Frequently asked questions
- What is the RAID Calculator?
- It is a browser-based tool that estimates the usable capacity, redundancy and storage efficiency of a RAID array based on the RAID level, disk count and disk size you enter. It also accounts for hot spares set aside for automatic rebuilds.
- How do I use this tool?
- Pick a RAID level, enter the number of disks and the capacity of a single disk, and optionally add hot spares, then read the calculated usable capacity, fault tolerance and efficiency. Everything runs in your browser, so nothing you type is sent or stored.
- Why does usable capacity matter compared to raw capacity?
- RAID levels trade raw disk space for redundancy, so a set of disks rarely gives you their full combined size as usable storage. Knowing usable capacity up front helps you size an array correctly and budget for the disks parity or mirroring will consume.
- How do I read the fault tolerance result?
- Fault tolerance shows how many disks can fail simultaneously without losing data: RAID 0 tolerates none, RAID 1 and 5 tolerate one, and RAID 6 tolerates two. Hot spares do not raise this number, they only speed up rebuilding after a failure has occurred.
- Does the calculated capacity match what my operating system will show?
- No, results are theoretical and use decimal terabytes, while filesystem formatting, controller overhead and binary (TiB) reporting will make the real usable figure somewhat lower. Treat the output as a planning estimate, not an exact guarantee.