RAID Calculator
Work out the usable capacity, parity overhead and efficiency of RAID 0, 1, 5, 6 and 10 arrays.
Usable capacity
3,072 GB
Raw capacity
4,096 GB
3 data drive(s) + 1 parity drive(s)
Space efficiency
75%
RAID 5 needs at least 3 drives
Overhead
1,024 GB
Capacity used for redundancy
RAID parity uses one drive (RAID 5) or two drives (RAID 6) per stripe. RAID 10 mirrors every drive, so half the raw capacity is usable.
Last updated: August 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
RAID capacity maths matters to anyone who runs more than one drive. Indian startups and production houses storing raw video, photo libraries or database backups use RAID 5 or RAID 6 to keep working when a drive dies, and the usable-capacity figure decides how many drives they must buy. Home NAS builders setting up media servers compare RAID 1's simple mirroring with RAID 5's efficiency before buying drives. System administrators planning server storage calculate the same numbers for procurement and budgeting, while cloud and DevOps engineers use RAID 0's full capacity for high-speed scratch space where data is disposable. Freelance editors and photographers with multi-drive enclosures check RAID 10 when they want both speed and redundancy. Because every level's usable space is a simple multiple of the per-drive size, this tool answers the 'how many drives do I actually need' question in seconds.
How to Use This Calculator
- Step 1: Select the RAID level — 0, 1, 5, 6 or 10.
- Step 2: Enter the number of drives in the array.
- Step 3: Enter the capacity of one drive and choose GB or TB.
- Step 4: Read the usable capacity, raw capacity, parity drive count and space efficiency.
Worked Example
A video editor in Mumbai stores client footage on four 1 TB drives configured as RAID 5. The calculator reports a raw capacity of 4,096 GB, of which 3,072 GB — three drives' worth — is usable, a 75% efficiency, with one parity drive protecting the data. Choosing RAID 6 with five 1 TB drives instead gives 3,072 GB usable out of 5,120 GB (60%), surviving two failures. A 4-drive RAID 10 array offers 2,048 GB usable at 50%, mirroring every drive, while RAID 0 with four 500 GB drives gives a full 2,000 GB with no protection at all.
Tips and Common Mistakes
- •Tip 1: Compare the usable capacity before buying drives — RAID 5's one-drive overhead is the popular balance of safety and space.
- •Tip 2: Larger drives change the arithmetic: four 2 TB drives in RAID 5 give 6 TB usable, not 8 TB.
- •Tip 3: RAID is not a backup — a failed controller, fire or ransomware still takes the whole array down with it.
- ✗Mistake 1: Building RAID 5 with only two drives — it needs at least three, and the calculator flags this.
- ✗Mistake 2: Building RAID 10 with an odd drive count, which leaves one drive with no mirror partner.
Frequently Asked Questions
What is RAID?
RAID combines multiple hard drives into one logical unit for speed, redundancy or both. RAID 0 stripes data across drives for speed, RAID 1 mirrors it for safety, and RAID 5, 6 and 10 mix both ideas.
Why is RAID 5 usable capacity one drive less?
RAID 5 keeps one parity drive's worth of redundancy across the array, so 4 drives of 1 TB each give 3 TB of usable space and 4 TB raw — a 75% efficiency. It can survive any single drive failing.
What is the difference between RAID 5 and RAID 6?
RAID 6 uses two drives of parity instead of one, so it survives two simultaneous drive failures but costs more capacity. With 5 drives of 1 TB, RAID 6 gives 3 TB usable (60% efficiency) versus 4 TB for RAID 5.
How much space does RAID 1 give me?
RAID 1 mirrors every drive exactly, so 2 drives of 1 TB give 1 TB usable — half the raw capacity. Data survives any single drive failure with zero rebuild risk, which is why it is common for boot drives.
How is RAID 10 capacity calculated?
RAID 10 mirrors each drive in pairs and stripes across the pairs, so usable capacity is exactly half the raw capacity. Four 1 TB drives give 2 TB usable, and the array needs an even number of drives.
What are the minimum drive requirements per RAID level?
RAID 0 and RAID 1 need 2 drives, RAID 5 needs 3, RAID 6 needs 4, and RAID 10 needs 4 (an even number). The calculator shows a friendly message when your drive count is below the minimum.
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