Estimate usable capacity, redundancy overhead, and resilience for common RAID levels. Private by design—everything runs in your browser.
RAID is not backup. RAID can keep storage online after a drive failure, but it does not protect against deletion, ransomware, silent corruption, theft, or site loss. Keep separate backups.
Inputs
Drive manufacturers usually advertise decimal TB, while operating systems often display binary TiB. An 8 TB drive may appear as about 7.28 TiB.
For safety, the calculator uses the smallest drive across the array.
Target capacity uses the selected drive-size unit. Hot spares are included in cost, not usable capacity.
Results
Results will appear here after you calculate.
Compare RAID Levels
RAID level
Min drives
Usable capacity formula
Fault tolerance
Best for
Avoid when
RAID 0
2
N x drive size
0
Speed / scratch data
Any important data
RAID 1
2
1 x drive size
1 drive
Simple mirror
Capacity efficiency matters
RAID 5
3
(N - 1) drives
1 drive
Small/medium arrays
Very large HDD arrays
RAID 6
4
(N - 2) drives
2 drives
Large HDD arrays
Write-heavy workloads
RAID 10
4 even
50% raw
1 worst-case; more if spread
Databases, VMs
Capacity-focused storage
RAID 50
6
Groups x (drives/group - 1)
1 per group best-case
Large arrays needing speed
Small arrays
RAID 60
8
Groups x (drives/group - 2)
2 per group best-case
Enterprise / large arrays
Budget builds
RAID Diagrams
RAID 0 striping
RAID 1 mirroring
RAID 5 distributed parity
RAID 6 double parity
RAID 10 mirrored stripes
RAID 50 / RAID 60 groups
How to Calculate RAID Capacity
RAID capacity is based on the smallest drive in the array. If drives are mixed, extra space on larger drives usually cannot be used inside the same RAID set.
Common formulas
RAID 0 usable = number of drives x smallest drive size
RAID 1 usable = smallest drive size
RAID 5 usable = (number of drives - 1) x smallest drive size
RAID 6 usable = (number of drives - 2) x smallest drive size
RAID 10 usable = (number of drives / 2) x smallest drive size
RAID 50 usable = groups x (drives per group - 1) x smallest drive size
RAID 60 usable = groups x (drives per group - 2) x smallest drive size
Mixed drive example
Four drives of 8 TB, 8 TB, 6 TB, and 10 TB in RAID 5 are calculated using 6 TB per drive, because the smallest drive limits the array.
The usable capacity is (4 - 1) x 6 TB = 18 TB before filesystem formatting and controller reservations.
Real-world results also depend on filesystem formatting, controller behavior, spare policies, and manufacturer units.
Which RAID Level Should I Choose?
Practical recommendations
Home NAS: RAID 1, RAID 5, or RAID 6 depending on drive count and risk tolerance.
Large HDD array: RAID 6 or RAID 60 for better rebuild safety.
VM/database server: RAID 10 for strong random I/O and simpler rebuilds.
Temporary scratch disk: RAID 0 when the data is disposable.
Budget capacity: RAID 5, with caution on very large HDD arrays.
Mission-critical storage: RAID 6/60 plus tested backups.
RAID 5 vs RAID 6 vs RAID 10
RAID 5 gives strong capacity efficiency but only tolerates one failed drive. It is best for smaller arrays and read-heavy workloads.
RAID 6 gives up another drive of capacity for two-drive fault tolerance, which is often worth it on large HDD arrays.
RAID 10 uses half the raw capacity but is usually the better fit for VMs, databases, and write-heavy workloads.
Release Updates
v1.1(May 19, 2026)
Added a RAID level comparison table for RAID 0, 1, 5, 6, 10, 50, and 60.
Added theoretical read/write gain, rebuild risk, and recommended use-case rows to the calculator results.
Added optional cost per drive, hot spare count, target usable capacity, and cost-per-usable-TB outputs.
Added binary TiB/GiB support alongside decimal TB/GB, plus a clear manufacturer-vs-OS unit explanation.
Added simple RAID diagrams and expanded guidance for capacity formulas, mixed drives, RAID selection, and RAID-is-not-backup planning.
Frequently Asked Questions
Do mixed drive sizes work?
Yes, but arrays are limited by the smallest drive in each redundancy set. This calculator conservatively uses the smallest drive across all disks. For example, 8 TB, 8 TB, 6 TB, and 10 TB drives in RAID 5 are calculated as four 6 TB drives.
Why do TB and TiB numbers differ?
Drive manufacturers usually advertise decimal TB, where 1 TB is 1,000 GB. Operating systems often display binary TiB, where 1 TiB is 1,024 GiB. That is why an 8 TB drive may appear as about 7.28 TiB.
Is RAID a backup?
No. RAID protects availability after some drive failures, but it does not protect against accidental deletion, ransomware, file corruption, theft, or site loss. Keep versioned backups on separate storage.
What are the minimum drive counts?
RAID 0: 2 · RAID 1: 2 · RAID 5: 3 · RAID 6: 4 · RAID 10: 4 (even) · RAID 50: ≥ 2 groups of ≥ 3 each · RAID 60: ≥ 2 groups of ≥ 4 each.
Why is RAID 10 “1+” for fault tolerance?
Each mirrored pair can lose at most one drive; in the best case several drives can fail (one per pair), but in the worst case only one failure is tolerated if two failures land in the same pair.
Is my data private?
Yes—calculations run entirely in your browser.
RAID Best Practices & Practical Standards
RAID improves availability and/or performance, but it is not a backup. Use the guidance below to plan safer, faster arrays.
1) Data Protection Basics
Follow 3-2-1 backups: 3 copies of data, on 2 different media, with 1 off-site/immutable copy.
Use a UPS to protect against write-hole corruption and sudden power loss. Prefer controllers or NVMe devices with power-loss protection.
Test restores, not just backups: Verify integrity and practice a restore workflow periodically.
2) Picking a RAID Level
Large SATA/NL-SAS drives (≥ 8 TB): prefer RAID 6 / RAIDZ2 or better; rebuilds are long and URE risk increases with size.
