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RAID Storage Calculator

Calculate usable storage capacity and overhead for RAID 0, 1, 5, 6, and 10.

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Inputs

TB

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Results

Usable Capacity
Protection/Overhead4
Fault Tolerance1 Disk

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Assumptions

  • Disk count should be a whole number and disk size should be a positive number.
  • All disks are assumed to be the same size, so the array is limited by the smallest member drive in real life.
  • Invalid RAID-level requirements, such as too few disks for RAID 5/6/10, return an invalid configuration state.

Sensitivity preview

Number of Disks Current: Usable Capacity 12 TB

Size per Disk -10%: Usable Capacity 10.8 TB

Size per Disk Current: Usable Capacity 12 TB

Formula: RAID 0: N*S. RAID 1: S. RAID 5: (N-1)*S. RAID 6: (N-2)*S. RAID 10: (N/2)*S.

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About this RAID Calculator

RAID (Redundant Array of Independent Disks) allows you to combine multiple hard drives to improve performance, data redundancy, or both. However, most RAID levels sacrifice some raw capacity to store 'parity' data for recovery. This calculator shows you exactly how much usable space you will get.

Who this calculator is for

  • Home-lab builders, NAS owners, and IT teams planning multi-disk arrays.
  • Anyone comparing RAID levels before buying drives or expanding storage.
  • Operators checking the tradeoff between usable capacity and fault tolerance.

When to use it

  • Use it to estimate usable capacity before building a RAID array.
  • Use it when comparing RAID 0, 1, 5, 6, and 10 for performance versus redundancy.
  • Use it to check how many disks and how much raw capacity a chosen RAID level will consume.

How to use this calculator

  1. Select your RAID Level (0, 1, 5, 6, 10).
  2. Enter the Number of Disks you plan to use.
  3. Enter the Size per Disk.
  4. The tool calculates Usable Capacity, Parity/Overhead, and Fault Tolerance.

Key assumptions

  • Disk count should be a whole number and disk size should be a positive number.
  • All disks are assumed to be the same size, so the array is limited by the smallest member drive in real life.
  • Invalid RAID-level requirements, such as too few disks for RAID 5/6/10, return an invalid configuration state.

Accuracy and testing

Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.

View accuracy page

How this calculator works

Each level has a different formula: * RAID 0: N × Disk Size (No loss, no safety). * RAID 1: Disk Size (Mirrored copies; with this calculator's model, usable capacity stays equal to one disk regardless of disk count). * RAID 5: (N-1) × Disk Size (1 disk used for parity). * RAID 6: (N-2) × Disk Size (2 disks used for parity). * RAID 10: (N/2) × Disk Size (Mirrored stripes).
RAID 0: N*S. RAID 1: S. RAID 5: (N-1)*S. RAID 6: (N-2)*S. RAID 10: (N/2)*S.

Inputs explained

RAID Level

The configuration type. RAID 5 is common for balance. RAID 6 offers high safety. RAID 10 offers speed and safety.

Disk Count

The total number of drives in the array.

Understanding your results

Usable Capacity is the actual space available for your files. Fault Tolerance tells you how many drives can fail before you lose data.

Example scenarios

Home NAS

4 disks, 4TB each. RAID 5. Usable: 12 TB. Parity: 4 TB. Can survive 1 disk failure.

High Speed Server

4 disks, 4TB each. RAID 10. Usable: 8 TB. Overhead: 8 TB. Can survive 1 disk per pair.

Key Features

  • Supports RAID 0, 1, 5, 6, 10
  • Calculates usable space vs parity
  • Fault tolerance indicator

Tips & Best Practices

  • Always use disks of the same size and speed for optimal performance.
  • RAID is not a backup! It protects against hardware failure, but not fire, theft, or accidental deletion.

Glossary of Terms

Parity
Data used to reconstruct information if a drive fails.
Striping
Spreading data across multiple disks to increase speed.
Mirroring
Duplicating data onto a second disk for redundancy.

Frequently Asked Questions

Which RAID is best for data safety?
RAID 6 allows for two simultaneous disk failures without data loss, making it very safe for large arrays. RAID 10 is also safe and offers faster rebuild times.
Does RAID replace backups?
No! RAID protects against drive failure to keep the system running. It does not protect against ransomware, file corruption, or catastrophic events. Always maintain separate backups.
Why do I need at least 3 disks for RAID 5?
RAID 5 stripes data and parity across all disks. You need a minimum of 3 drives to distribute the parity information effectively while maintaining usable capacity.