RAID Calculator
Calculate usable storage capacity, storage efficiency, and fault tolerance for RAID 0, 1, 5, 6, and 10 - a RAID capacity calculator for planning a NAS or server array before you buy the drives.
Single-disk fault tolerance with good capacity
Recommended Settings
Pro Tips
- •RAID 0 gives you full capacity and speed but zero redundancy - a single drive failure loses everything
- •RAID 5 is the most common balance of capacity and protection, tolerating one drive failure with only one disk's worth of overhead
- •RAID 6 costs two disks' worth of capacity but survives two simultaneous failures, which matters more as array size (and rebuild time) grows
- •RAID 10 rebuilds fastest after a failure since it only needs to re-mirror one disk, not recalculate parity across the whole array
Most Popular
RAID 5 with 4-6 disks is the most common home NAS and small-server configuration
When to Use This Tool
Compare usable capacity and redundancy across RAID levels before choosing drives for a home or office NAS.
Estimate how many and what size drives you need to hit a target usable capacity.
See the capacity-versus-redundancy trade-off between RAID 5, 6, and 10 side by side.
Check the fault tolerance of a proposed array before committing to a RAID level.
How It Works
Pick a RAID level and enter the number of disks and the size of each disk
Usable capacity is calculated from the RAID level's formula - for example, RAID 5 reserves one disk's worth of capacity for parity
Storage efficiency is usable capacity divided by raw (total) capacity
Fault tolerance reflects how many disks can fail before the array loses data
100% Private
Files never leave your device. All processing happens locally in your browser.
Lightning Fast
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Open Source
Built with verified, open-source libraries. Fully transparent.
Frequently Asked Questions
How is RAID 5 usable capacity calculated?
RAID 5 usable capacity is (number of disks - 1) x disk size - one disk's worth of space is used for parity data, regardless of which physical disk it's spread across.
What's the difference between RAID 5 and RAID 6?
RAID 5 uses one disk's worth of parity and tolerates one disk failure. RAID 6 uses two disks' worth of parity and tolerates two simultaneous failures, at the cost of more capacity overhead.
Why does RAID 10 need an even number of disks?
RAID 10 is built from mirrored pairs (RAID 1) that are then striped together (RAID 0), so disks are always added two at a time - one pair per mirror.
Is a RAID capacity calculator the same as this tool?
Yes - calculating RAID capacity is exactly what this tool does, alongside storage efficiency and fault tolerance for the same setup.
Does RAID replace backups?
No. RAID protects against a drive failure, but not against accidental deletion, ransomware, or a fire or theft affecting the whole array - a separate backup is still necessary.
Is my data sent to a server?
No. All calculations happen instantly in your browser using JavaScript - nothing is transmitted anywhere.