RAID Storage Capacity Calculator
Estimate theoretical RAID 0, 1, 5, 6 or 10 capacity with identical drives and optional dedicated spares. Separate raw, usable, redundancy and spare capacity.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Subtract dedicated spares from the installed count. Apply the selected layout to the active equal-sized drives: striping uses all, an all-drive mirror uses one drive-equivalent, parity layouts reserve one or two, and paired mirrors use half.
Usable capacity=drive capacity×data-drive equivalents; RAID 5 uses N−1, RAID 6 N−2, RAID 10 N/2
Worked example
Four 4 TB drives with no spares provide 16 TB in RAID 0, 4 TB in an all-drive RAID 1 mirror, 12 TB in RAID 5, 8 TB in RAID 6 and 8 TB in RAID 10, before formatting.
Assumptions and input details
Identical capacity per drive; minimum two active drives for RAID 0/1, three for RAID 5 and four for RAID 6. RAID 10 requires an even active count of at least four. RAID 1 here means all active drives mirror one copy, not several separate mirror volumes. Dedicated spares contribute no usable or active parity capacity. TB is decimal and TiB is binary. Filesystem metadata, system partitions, controller limits, reserved space, mixed-size drives, SHR/ZFS layouts and performance are excluded. Failure tolerance describes the layout, not a guarantee during rebuild; RAID does not replace a backup.
References: Western Digital RAID capacity · Seagate RAID technology
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
One byte is eight bits. Decimal prefixes (k, M, G, T, P, E) use powers of 1000. Binary prefixes (Ki, Mi, Gi, Ti, Pi, Ei) use powers of 1024. Transfer rates are per second.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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