RAID capacity calculator

Estimate usable RAID capacity from equal-size drives and your chosen stripe, mirror or parity layout.

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Drive count

Capacity of each smallest drive

More inputs and assumptions

RAID layout

Answer

…

Estimate usable RAID capacity from equal-size drives and your chosen stripe, mirror or parity layout.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

RAID 0 = N drives; RAID 1 = one drive; RAID 5 = N − 1; RAID 6 = N − 2; RAID 10 = N/2. Multiply by the smallest drive capacity. Excludes metadata, formatting, hot spares and controller differences. RAID is not a backup.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using RAID capacity calculator

Estimate usable RAID capacity from equal-size drives and your chosen stripe, mirror or parity layout.

Next: Download time calculator

A worked example

Example inputs: drive count = 4, capacity of each smallest drive = 2, raid layout = 2. Modeled usable capacity = 6.

Before you use the result

Example results for drive count

These examples use Capacity of each smallest drive: 2; RAID layout: RAID 5: single parity. They are reference calculations, not recommended settings.

Drive count	Modeled usable capacity
4	6
8	14

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