ip subnetting calculator

What this IP subnetting calculator does

This IP subnetting calculator is designed for students, network engineers, help desk teams, and anyone preparing for networking certifications. Given an IP address and prefix length, it computes all the key values you need for real-world planning: network address, broadcast address, subnet mask, wildcard mask, host range, total addresses, and usable hosts.

If you provide a second prefix (for example splitting a /24 into /26), the tool also builds a subnet table so you can quickly see each subnet boundary and host range. This is especially useful for VLAN design, branch office rollouts, and clean IP documentation.

Why subnetting matters

Subnetting helps you divide a large network into smaller, manageable segments. Done well, it improves performance, security, and operational clarity.

• Better traffic control: Broadcast domains stay smaller and cleaner.
• Improved security: Segmentation makes policy enforcement easier.
• Scalability: Structured address plans are easier to grow over time.
• Troubleshooting speed: Well-defined subnets simplify incident response.

Quick CIDR reference

Common prefixes and host capacity

• /24 = 256 total addresses, 254 usable hosts
• /25 = 128 total addresses, 126 usable hosts
• /26 = 64 total addresses, 62 usable hosts
• /27 = 32 total addresses, 30 usable hosts
• /28 = 16 total addresses, 14 usable hosts
• /29 = 8 total addresses, 6 usable hosts
• /30 = 4 total addresses, 2 usable hosts
• /31 = 2 total addresses, typically both usable on point-to-point links (RFC 3021)
• /32 = 1 address (single host route)

How to use this subnet calculator

Step-by-step

1. Enter a valid IPv4 address (for example, 10.50.4.19).
2. Enter the CIDR prefix (for example, 22 for /22).
3. Click Calculate Subnet.
4. Review the computed network details.
5. Optional: enter a new prefix to split into smaller subnets and generate a subnet table.

Manual check example

Suppose your IP is 192.168.10.44/24. With a /24 prefix:

• Subnet mask is 255.255.255.0
• Network address is 192.168.10.0
• Broadcast address is 192.168.10.255
• Usable host range is 192.168.10.1 to 192.168.10.254

If you split that /24 into /26 networks, you get 4 subnets of 64 addresses each: .0/26, .64/26, .128/26, and .192/26.

Common subnetting mistakes to avoid

• Confusing total addresses with usable hosts.
• Assigning the network or broadcast address to hosts.
• Forgetting special behavior of /31 and /32 networks.
• Using inconsistent subnet sizes without a VLSM plan.
• Skipping documentation after subnet changes.

Final thoughts

A fast, accurate IP subnetting calculator saves time and prevents costly addressing mistakes. Whether you're studying for CCNA, building a home lab, or designing enterprise networks, mastering subnet boundaries and host ranges is foundational networking skill.

Bookmark this page and use it whenever you need quick IPv4 subnet calculations and clean subnet split planning.