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Network Engineer

RAID Capacity Calculator

Use this raid capacity calculator entirely in your browser.

ResultUsable capacity: 32 TB

Raw capacity: 48 TB.

Nominal failure tolerance: Two drives.

Calculations happen locally in your browser.

RAID is not a backup

The calculator assumes equal-size drives and reports nominal decimal capacity. Filesystem metadata, hot spares, controller rules, mixed drive sizes, and vendor-reserved space can reduce usable capacity. RAID improves availability; it does not replace separate, tested backups.

How to use this calculator

  1. Enter the labelled values and review the live result.
  2. Review the live result and use Copy result when you need to share it.

How the calculation works

Usable capacity applies the selected RAID layout's parity or mirroring rule to equal-size drives.

Formula

Usable capacity applies the selected RAID layout's parity or mirroring rule to equal-size drives.

Step-by-step calculation

  1. Enter the labelled values and review the live result.
  2. Usable capacity applies the selected RAID layout's parity or mirroring rule to equal-size drives.
  3. Check the displayed result, then copy it if needed.

Worked example

Six 8 TB drives in RAID 6 provide 32 TB nominal usable capacity.

Methodology and review

Who this is for

NAS builders and administrators comparing common RAID layouts.

Inputs and units

  • Drive count
  • Capacity per drive
  • RAID level

Method

Usable capacity is calculated from equal-size drives using the selected RAID layout's mirroring or parity rule; raw capacity and drive-failure tolerance are shown separately.

Worked example

Four 4 TB drives in RAID 5 provide 12 TB nominal usable capacity.

Assumptions

  • All drives contribute the capacity of the smallest drive entered.
  • The result is nominal capacity before filesystem, metadata, reserve, and vendor formatting overhead.

Common mistakes

  • Calling RAID a backup
  • Assuming mixed drives retain all capacity

Limitations

  • RAID is not a backup and does not protect against deletion, corruption, theft, or a site-wide failure.
  • Controller-specific layouts, hot spares, rebuild risk, and mixed drive sizes need vendor documentation.

How this tool was checked

Unit tests exercise the supported RAID 0, 1, 5, 6, and 10 capacity rules and reject invalid drive counts.

Related tools

Calculation review: 21 August 2026. Published by Goldwave Dynamics Limited. This is an internal product review, not an independent certification.

Risk guidance

Frequently asked questions

Does this tool send my inputs anywhere?

No. The interactive calculation runs in your browser and this site does not submit tool inputs to a backend.

How should I use the result?

Check that the entered units and values match your situation, especially around dates, breaks, and rounding.

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