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RAID Calculator

Calculate usable storage capacity, fault tolerance, and performance characteristics for different RAID levels.

Reviewed by Christopher FloiedPublished Updated

This free online raid calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

Total number of disks in the array

Capacity of each individual disk in terabytes

Results

Usable Capacity

6 TB

How to Use This Calculator

1

Enter your input values

Fill in all required input fields for the RAID Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

2

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

3

Read the results

The RAID Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

4

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

Formula Reference

RAID Calculator Formula

See calculator inputs for the governing equation

Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.

When to Use This Calculator

  • •Use the RAID Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
  • •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
  • •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
  • •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

About This Calculator

The RAID Calculator is a free, browser-based calculation tool for engineers, students, and technical professionals. Calculate usable storage capacity, fault tolerance, and performance characteristics for different RAID levels. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.

About RAID Calculator

The RAID Calculator computes the usable storage capacity for different RAID configurations. RAID (Redundant Array of Independent Disks) combines multiple physical disks into a single logical unit to improve performance, reliability, or both. This calculator shows how much usable storage you get after accounting for parity and mirroring overhead for RAID levels 0, 1, 5, 6, and 10.

The Math Behind It

RAID technology was introduced in 1988 to combine inexpensive disks into arrays that offer better performance and reliability than single expensive drives. Different RAID levels trade off between capacity, performance, and fault tolerance. RAID 0 stripes data across all disks with no redundancy. It provides maximum capacity (N * D) and the best read/write performance, but any single disk failure destroys all data. It is suitable only for non-critical data where performance is paramount. RAID 1 mirrors data across two disks. Usable capacity equals one disk (D). It provides excellent read performance and survives one disk failure but wastes 50% of total capacity. It is ideal for operating system drives and critical databases. RAID 5 stripes data with distributed parity across at least 3 disks. Usable capacity is (N-1) * D, with one disk's worth of capacity used for parity. It survives one disk failure and provides good read performance. RAID 5 is the most popular level for general-purpose storage. RAID 6 extends RAID 5 with double distributed parity, requiring at least 4 disks. Usable capacity is (N-2) * D. It survives two simultaneous disk failures, making it safer for large arrays where rebuild times are long. RAID 10 combines mirroring and striping, requiring at least 4 disks in pairs. Usable capacity is (N/2) * D. It provides the best performance among redundant RAID levels and can survive multiple disk failures as long as both disks in a mirror pair do not fail simultaneously.

Formula Reference

RAID Capacity

RAID 0: N*D, RAID 1: D, RAID 5: (N-1)*D, RAID 6: (N-2)*D, RAID 10: (N/2)*D

Variables: N = number of disks, D = disk size

Worked Examples

Example 1: RAID 5 with four 2TB drives

Four 2TB drives configured in RAID 5.

Step 1:RAID 5 formula: (N - 1) * D
Step 2:Usable capacity: (4 - 1) * 2 = 6 TB
Step 3:Overhead: 1 disk equivalent (2 TB) used for parity
Step 4:Capacity efficiency: 6/8 = 75%

The RAID 5 array provides 6 TB of usable storage from 8 TB raw capacity, with single-disk fault tolerance.

Common Mistakes & Tips

  • !Mixing disks of different sizes in RAID; the array uses the smallest disk size for all calculations.
  • !Choosing RAID 0 for important data without understanding there is zero fault tolerance.
  • !Not considering rebuild time; large RAID 5 arrays may take days to rebuild, during which a second failure causes data loss.

Related Concepts

Byte Conversion Calculator

Convert between different data storage units.

Bandwidth Calculator

Calculate data transfer rates and bandwidth requirements.

Frequently Asked Questions

Which RAID level should I use?

For critical data with good performance: RAID 10. For capacity-efficient redundancy: RAID 5 (small arrays) or RAID 6 (large arrays). For maximum performance without redundancy: RAID 0. Never use RAID 0 for data you cannot afford to lose.

Is RAID a backup?

No. RAID protects against disk hardware failure, but it does not protect against file deletion, corruption, ransomware, or controller failure. Always maintain separate backups regardless of RAID level.