RAID Price Per TB Calculator
Enter your Number of Drives, Drive Capacity, Price Per Drive, and RAID Level. The calculator shows your usable capacity after RAID overhead and the true cost per usable TB — the only figure that matters when comparing configurations.
Configuration
All RAID Levels — Cost Comparison
Enter values above and click Calculate to populate this table with your drive pricing.
| RAID Level | Usable Capacity | Cost Per Usable TB | Overhead | Fault Tolerance | Best For |
|---|---|---|---|---|---|
| RAID 0 | — | — | 0% | None | Temp data, scratch space |
| RAID 1 | — | — | 50% | 1 per pair | OS drives, critical data |
| RAID 5 | — | — | 1 drive | 1 drive | File servers, general use |
| RAID 6 | — | — | 2 drives | 2 drives | Large arrays, archives |
| RAID 10 | — | — | 50% | 1 per mirror | Databases, high performance |
| RAID 50 | — | — | 2 drives | 1 per group | Large databases, video editing |
| RAID 60 | — | — | 4 drives | 2 per group | Highest reliability |
Why Cost Per Usable TB Matters
The sticker price of a hard drive tells you very little about the true cost of your storage. Once you factor in RAID overhead, the cost per usable terabyte can be dramatically higher than the raw price per drive suggests. A 12-drive array with 4 TB drives at $80 each costs $960 in hardware — but under RAID 6, only 10 drives worth of capacity is usable, bringing the effective cost to $24/TB instead of the misleading $20/TB raw figure. Learn more: calculate RAID usable capacity and overhead.
RAID 1 and RAID 10 are the most expensive configurations by cost per usable TB because they mirror every byte, resulting in 50% overhead. On an 8-drive 4 TB array at $100/drive, RAID 10 gives you 16 TB usable at $50/usable TB — double the raw rate. RAID 5 is more efficient, sacrificing only one drive's worth of capacity to parity, typically adding 12–33% overhead depending on the drive count. Check out our compare storage cost across tiers.
RAID 6 adds a second parity drive for resilience against two simultaneous failures, which matters significantly for large arrays. With 12 drives, RAID 6 overhead is just 16.7%, making it surprisingly efficient for the protection it provides. For NAS and small business servers, comparing the cost per usable TB across configurations is the single most useful metric when making a purchasing decision. See also: StorageMath storage tools.
Frequently Asked Questions
How is cost per usable TB calculated?
Total drive cost (drives × price each) is divided by the usable capacity after RAID overhead. For 8 × 4 TB drives at $100/drive under RAID 5: total cost = $800, usable = 7 × 4 TB = 28 TB, so cost per usable TB = $800 ÷ 28 = $28.57/TB.
Which RAID level is cheapest per usable TB?
RAID 0 is always cheapest because it uses 100% of raw capacity, but provides no fault tolerance. Among protected configurations, RAID 5 and RAID 6 with many drives achieve the best cost efficiency — overhead drops as you add more drives (e.g., RAID 6 on 12 drives is only 16.7% overhead).
Does this include the hot spare cost?
Yes. Hot spare drives are purchased and their cost is included in the total. However, they contribute no usable capacity until a failure triggers a rebuild — so they increase cost per usable TB directly proportional to their count.
Important Notes
- Calculations are based on nominal drive capacity. Actual formatted capacity is typically 5–8% lower depending on the vendor.
- Hot spare drives add to total cost but provide no usable capacity. Their cost is included in the per-TB figure.
- RAID 5 with drives 4 TB or larger carries elevated rebuild risk. RAID 6 or RAID 10 is recommended for large drives in production.
- This calculator covers hardware cost only. RAID controller, enclosure, power, cooling, and maintenance costs are not included.