RAID Capacity Calculator | Usable Disk Space

RAID capacity calculator for RAID 0, 1, 5, 6 and 10: enter disk count and size to get usable space, fault tolerance and write penalty. Free. Designed specifically for developers and professionals, this free online calculator runs entirely in your browser to process tasks quickly and securely. Enjoy unlimited usage with no data tracking and no registration required.

Also known as: raid capacity calculator · raid calculator online · usable storage raid 5 · raid 6 capacity calculator · raid 10 usable space · raid write penalty · nas storage calculator · raid fault tolerance calculator

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Array Configuration

RAID level

One parity disk worth of capacity. Survives one failure.

Number of disks

Minimum 3 for RAID 5.

Size per disk

Use the size printed on the drive. Mixed sizes are limited to the smallest disk in the array.

Capacity is only half the decision. The write penalty column tells you how many physical operations one logical write costs, which is why RAID 6 is a poor fit for a write-heavy database and a good fit for an archive.

Capacity Result

Usable capacity, fault tolerance and a comparison across RAID levels will appear here.

About RAID Capacity Calculator

Work out how much usable space a disk array actually gives you before buying the drives. Enter a RAID level, a disk count and a disk size, and the calculator returns usable capacity in both decimal and binary units, how many disks can fail, the percentage lost to redundancy, and the write penalty each level carries.

Key Features

Covers RAID 0, 1, 5, 6 and 10 with the minimum disk count and even-disk rules enforced per level
Reports usable capacity in decimal TB and binary TiB, because drive vendors and operating systems disagree
Shows fault tolerance in disks, and flags RAID 0 explicitly as having none
Lists the write penalty for each level, the multiplier of physical operations per logical write
Compares your disk count across every valid RAID level side by side in one table
Copy or download the full report for a hardware purchase request or a design document

Use Cases

Price out a NAS for a small studio in Austin and see whether RAID 6 leaves enough usable space
Decide between RAID 10 and RAID 5 for a Postgres server where write throughput matters more than capacity
Explain to a finance reviewer why 8 disks of 16 TB does not give 128 TB of usable storage
Check how much capacity a rebuild-tolerant RAID 6 array costs against RAID 5 on the same hardware
Size a backup target where efficiency matters more than write speed
Confirm an existing array has the fault tolerance a compliance control claims it does

Supported Formats

RAID 0, 1, 5, 6 and 10

Disk sizes in GB or TB

Output in decimal TB and binary TiB

Related Keywords

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Why does my 4 TB drive show up as 3.64 TB?

Drive manufacturers sell capacity in decimal units where 1 TB is 1,000,000,000,000 bytes, while Windows and most tools report binary units where 1 TiB is 1,099,511,627,776 bytes and is often mislabeled TB. Dividing one by the other gives roughly 0.909, so a 4 TB drive reports as about 3.64 TiB and a 16 TB drive as about 14.55 TiB. Nothing is missing and no space was lost to formatting, the two numbers are simply counting in different bases. This calculator prints both so the figure you plan with matches the figure your operating system will show.

Calculated in your browser

All arithmetic runs locally in JavaScript. Nothing about your storage plans or hardware inventory is sent anywhere.

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Frequently asked questions

What is RAID Capacity Calculator used for?

RAID capacity calculator for RAID 0, 1, 5, 6 and 10: enter disk count and size to get usable space, fault tolerance and write penalty. Free.

Is RAID Capacity Calculator free to use?

Yes. RAID Capacity Calculator is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use RAID Capacity Calculator?

No. RAID Capacity Calculator works immediately in your browser with no signup, login, or email address required.

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