Skip to content
ToolStaxx Tools that stack up
Project SheetAll tools

ToolStaxx guide

How to calculate usable RAID capacity

RAID usable capacity depends on drive count, drive size and RAID level.

Open RAID Capacity Calculator Browse Files

Quick answer

RAID usable capacity depends on drive count, drive size and RAID level.

How to do it

  1. RAID 0 uses all drive capacity but has no redundancy.
  2. RAID 1 mirrors data and usually gives one drive of usable capacity.
  3. RAID 5 commonly uses one drive for parity.
  4. RAID 6 commonly uses two drives for parity. RAID is not a backup.

Worked example

Four 4 TB drives in RAID 5 gives about 12 TB before formatting and filesystem overhead.

Common mistakes

  • Thinking RAID is a backup.
  • Ignoring rebuild risk and filesystem overhead.
  • Mixing different drive sizes without checking behaviour.

When this is not suitable

Do not treat any quick estimate as a final specification where safety, contracts, regulations or expensive purchases depend on it.

Related next tools

Next useful tech and file tools for this task.

TechDownload Time CalculatorEstimate download time from file size and connection speed. FilesData Transfer CalculatorConvert common file sizes between MB, GB and TB. TechIPv4 Subnet CalculatorCalculate network address, broadcast address, usable host range and host count from IPv4/CIDR. FilesJSON Formatter and ValidatorPaste JSON to validate, format, minify and copy clean output.

Keep the result together

Use the calculator first, then add the result to a Project Sheet if you need a clean printable summary.

Open Project Sheet Builder