CIDR Calculator Form
Example Data Table
| Input CIDR | Network | First Host | Last Host | Broadcast | Usable Hosts |
|---|---|---|---|---|---|
| 192.168.10.14/27 | 192.168.10.0 | 192.168.10.1 | 192.168.10.30 | 192.168.10.31 | 30 |
| 10.0.4.52/22 | 10.0.4.0 | 10.0.4.1 | 10.0.7.254 | 10.0.7.255 | 1022 |
| 172.16.8.200/29 | 172.16.8.200 | 172.16.8.201 | 172.16.8.206 | 172.16.8.207 | 6 |
| 203.0.113.25/30 | 203.0.113.24 | 203.0.113.25 | 203.0.113.26 | 203.0.113.27 | 2 |
Formula Used
1. Subnet mask from prefix: A prefix of /n means the first n bits are network bits and the remaining 32 - n bits are host bits.
2. Network address: Network = IP AND Subnet Mask
3. Wildcard mask: Wildcard = 255.255.255.255 XOR Subnet Mask
4. Broadcast address: Broadcast = Network OR Wildcard
5. Total addresses: 2^(32 - Prefix)
6. Usable hosts: Usually 2^(32 - Prefix) - 2. For /31, two addresses are commonly usable. For /32, one address exists.
7. Child subnet count: 2^(Child Prefix - Base Prefix)
How to Use This Calculator
- Enter an IPv4 address with prefix length, such as 192.168.10.14/27.
- Optionally enter a larger split prefix to preview smaller child subnets.
- Choose how many child subnet rows you want to preview.
- Press Calculate CIDR Range to display the result section above the form.
- Review the summary table, binary values, graph, and subnet preview.
- Use the export buttons to save the report as CSV or PDF.
Frequently Asked Questions
1. What does CIDR mean?
CIDR stands for Classless Inter-Domain Routing. It uses prefix lengths, such as /24 or /27, to describe how many bits belong to the network portion of an IPv4 address.
2. Why is the network address different from my input IP?
Your input may be a host inside the subnet. The calculator applies the subnet mask to find the base network address that represents the whole address block.
3. What is the difference between total addresses and usable hosts?
Total addresses include every address in the block. Usable hosts usually exclude the network and broadcast addresses, except special cases such as /31 and /32.
4. Why does /31 show two usable addresses?
/31 subnets are commonly used on point-to-point links. In that case, both addresses can be treated as usable because a broadcast address is usually unnecessary.
5. What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. It is often used in routing and access control rules to describe which bits may vary.
6. Can this page split one subnet into smaller subnets?
Yes. Enter a larger split prefix, such as /29 after a /27 input, and the calculator previews child networks, hosts, and broadcast addresses.
7. Does this calculator work with IPv6?
No. This version is designed for IPv4 CIDR analysis. IPv6 addressing uses a different address size, notation style, and planning workflow.
8. When should I export CSV or PDF?
Use CSV when you want spreadsheet analysis or inventory imports. Use PDF when you want a clean report for reviews, documentation, or team handoff.