IP Address CIDR Calculator

Example Data Table

Formula Used

Subnet mask: the prefix sets the first network bits to 1. The remaining host bits are 0.

Network address: Network = IP address AND subnet mask

Wildcard mask: Wildcard = NOT subnet mask

Broadcast address: Broadcast = Network address OR wildcard mask

Total addresses: Total = 2^(32 - prefix)

Usable hosts: Usable = Total - 2 for normal subnets. A /31 has 2 usable point-to-point addresses. A /32 has 1 host route.

Child prefix: Child prefix = Parent prefix + ceiling(log2(required subnet count))

How to Use This Calculator

1. Enter an IPv4 address, such as 192.168.1.25.
2. Add a slash prefix, such as /24, or enter prefix separately.
3. Enter required hosts if you want a size recommendation.
4. Enter a subnet split count if you want child subnet examples.
5. Press the calculate button.
6. Review the result above the form.
7. Use CSV export for spreadsheet records.
8. Use PDF export for reports, tickets, or client notes.

Why CIDR Planning Matters

CIDR notation keeps IPv4 planning compact and clear. It shows an address and prefix in one short value. A prefix tells how many leading bits belong to the network. The remaining bits describe host space. This calculator converts that idea into practical network details.

A good CIDR plan prevents wasted addresses. It also reduces routing noise. Smaller, accurate subnets are easier to document. They are easier to audit too. Teams can compare masks, wildcard masks, usable ranges, and broadcast addresses before making changes. That helps avoid overlap between offices, servers, labs, and cloud networks.

How The Results Help

The network address shows the first address in the block. The broadcast address shows the final address for normal IPv4 subnets. The first usable and last usable values show the common host range. The total addresses value includes every address in the block. The usable hosts value removes reserved network and broadcast addresses when needed.

Binary output is useful for learning. It shows why a prefix creates a specific boundary. Hex output helps when logs or low level tools display addresses in another format. The wildcard mask helps with routing rules, access lists, and network matching.

Advanced Planning Tips

Start with the number of hosts you need. Add space for growth. Then choose the smallest prefix that supports that size. Avoid choosing a very large subnet only because it feels safe. Large unused ranges can create future conflicts.

When splitting a subnet, count the extra bits needed. Each added bit doubles the subnet count and halves each child block. This calculator shows a child prefix and sample child ranges. Use those samples to build consistent documentation.

Always check special cases. A /32 points to one host address. A /31 is often used for point to point links. Older designs may still avoid /31 for hosts. Match your result to your router, firewall, and provider rules.

Use exports for records. Save CSV files for spreadsheets. Save PDF summaries for tickets, change plans, or client notes. Keep old calculations with dates. Clear records make later troubleshooting much faster. Review records during audits. Update them whenever network ownership or policy shifts.

FAQs