How Much Storage in RAID?
Quick answer: it depends on your RAID level. Use our calculator or reference the formulas below to find your usable capacity.
✓ All RAID level formulas
✓ Quick capacity examples
✓ Efficiency percentages
Distributes parity across all drives. Survives one drive failure. Good balance of capacity and protection.
Usable Capacity
11.82 TB
75.0% storage efficiency
RAID level comparison
| Level | Min | Fault tolerance | Capacity formula |
|---|---|---|---|
| RAID 0 | 2 | None | N × Size |
| RAID 1 | 2 | N−1 drives | 1 × Size |
| RAID 5 | 3 | 1 drive | (N−1) × Size |
| RAID 6 | 4 | 2 drives | (N−2) × Size |
| RAID 10 | 4 | 1/mirror pair | (N÷2) × Size |
| RAID 50 | 6 | 1/sub-array | (N−2) × Size* |
| RAID 60 | 8 | 2/sub-array | (N−4) × Size* |
| JBOD | 1 | None | N × Size |
| SHR | 1 | 1 drive (SHR-1) | ≈(N−1) × Size |
* Assumes 2 sub-arrays. N = number of drives.
RAID Capacity Formulas by Level
Each RAID level balances capacity, performance, and redundancy differently. Here are the usable storage formulas for every common RAID level:
RAID 0: N × Drive Size (100% — no redundancy)
RAID 1: 1 × Drive Size (50% with 2 drives)
RAID 5: (N-1) × Drive Size (67–93%)
RAID 6: (N-2) × Drive Size (50–88%)
RAID 10: N/2 × Drive Size (50% — needs even drive count)
RAID 50: (N - spans) × Drive Size
RAID 60: (N - 2×spans) × Drive Size
Quick Reference: 4 × 4TB Drives
RAID 0: 16TB usable (0 fault tolerance)
RAID 5: 12TB usable (1 drive fault tolerance)
RAID 6: 8TB usable (2 drive fault tolerance)
RAID 10: 8TB usable (1 per mirror pair)
Choosing the Right RAID Level
- Maximum capacity: RAID 0 (but no protection — only for expendable data)
- Simple protection: RAID 1 for 2 drives, RAID 5 for 3–6 drives
- Maximum protection: RAID 6 for large drives, RAID 10 for write-heavy workloads
- Best all-around: RAID 6 for NAS/file servers, RAID 10 for databases
💾 Real vs. Advertised Capacity
Drive manufacturers use decimal TB (1TB = 1,000,000,000,000 bytes), but operating systems use binary TB (1TB = 1,099,511,627,776 bytes). A “4TB” drive shows ~3.64TB in your OS. Subtract ~7–8% from advertised capacity for real-world numbers.