RAID Capacity Calculator
Usable capacity and fault tolerance.
Enter your values
Enter the number of disks you are working with.
Enter the disk size in TB.
Choose one of: RAID 0, RAID 1, RAID 5, RAID 6, RAID 10.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Usable capacity
- 40 TB
- Raw capacity
- 48 TB
- Redundancy overhead
- 16.7%
- Disk failures tolerated
- 1
Quick answer
RAID trades raw capacity for redundancy, with usable space depending on the level chosen.
RAID 5 usable = (n − 1) × disk size
At a glance
| What it does | Usable capacity and fault tolerance. |
|---|---|
| Category | Technology |
| Inputs needed | Number of disks, Disk size, RAID level |
| Main output | Usable capacity |
| Formula | RAID 5 usable = (n − 1) × disk size |
| Cost | Free — no sign-up, no download |
How to use the RAID Capacity Calculator
- 1Enter disk count and size.
- 2Choose the RAID level.
- 3Compare usable capacity with fault tolerance.
Inputs explained
- Number of disks
- Enter the number of disks you are working with.
- Disk size(TB)
- Enter the disk size in TB.
- RAID level
- Choose one of: RAID 0, RAID 1, RAID 5, RAID 6, RAID 10.
Worked example
Using the values the calculator loads with:
Inputs
- Number of disks6
- Disk size8 TB
- RAID levelRAID 5
Results
- Usable capacity40 TB
- Raw capacity48 TB
- Redundancy overhead16.7%
- Disk failures tolerated1
Frequently asked questions
Is RAID a backup?
No — it survives disk failure, not deletion, fire or ransomware.
RAID 5 or 6?
Use RAID 6 for disks over 4 TB because rebuild times are long.
What do I need to enter into the RAID Capacity Calculator?
Just 3 values: number of disks, disk size, raid level. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the RAID Capacity Calculator work out the answer?
RAID trades raw capacity for redundancy, with usable space depending on the level chosen. It applies the formula RAID 5 usable = (n − 1) × disk size and shows the working so you can check each step by hand.
Is the RAID Capacity Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.