SwiftTools
Free Network Planning Tool

IP Subnet Calculator

Calculate CIDR notation, subnet masks, network ranges, and broadcast addresses instantly. Perfect for network design, CCNA study, and IP address planning.

/0 - /32
CIDR Support
< 1ms
Calculation Speed
JSON, CSV
Export Formats
100%
Accuracy

Instant Calculations

Real-time subnet calculations with binary visualization. No page reloads—see results as you type with sub-millisecond response times.

Subnet Splitting

Divide networks into equal subnets automatically. Perfect for VLSM (Variable Length Subnet Masking) and network segmentation planning.

CCNA Study Ready

Complete with binary representations, wildcard masks, and CIDR cheat sheets. Essential tool for Cisco certification exam preparation.

Understanding IP Subnetting

Subnetting is the practice of dividing a network into two or more smaller networks (subnets) to improve performance and security. By using our subnet calculator, you can quickly determine network addresses, broadcast addresses, and available host ranges without manual binary calculations.

How to Use This Subnet Calculator

1. Basic Subnet CalculationEnter any IP address and select CIDR prefix to see network details, usable ranges, and broadcast address.
2. Split NetworksUse the Subnet Splitter to divide a large network into smaller, equal-sized subnets for different departments.
3. Reference TablesCheck the CIDR Cheat Sheet for quick reference of common subnet masks and their use cases.
4. Binary LearningView binary representations to understand how subnet masks work at the bit level.

Common Subnetting Scenarios

  • •Point-to-Point Links: Use /30 or /31 subnets to conserve IP addresses on router-to-router connections
  • •Small Offices: /28 subnets provide 14 usable hosts—perfect for branch offices with printers, PCs, and phones
  • •Data Centers: /29 or /28 subnets for server racks with room for growth
  • •Guest WiFi: /23 or /22 subnets to handle large numbers of transient devices

Frequently Asked Questions About Subnetting

Network Engineering Resources

Master subnetting with these essential formulas and concepts used by network engineers worldwide.

Usable Hosts Formula

2^(32 - CIDR) - 2

Subtract 2 for network and broadcast addresses

Subnet Count Formula

2^borrowed_bits

Must be power of 2 (2, 4, 8, 16...)

Block Size

256 - subnet_mask_octet

Helps quickly identify network boundaries

Magic Number

256 - interesting_octet

The increment between subnet IDs

All calculations performed locally in your browser. No data is sent to servers. Compatible with RFC 950, RFC 1878, and RFC 3021 (/31) standards.

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