Calculate subnet details
Use CIDR or a subnet mask. Add a new prefix to split the base network into smaller subnets.
Example data table
| Input IP | Prefix | Network | Broadcast | Usable Hosts |
|---|---|---|---|---|
| 192.168.10.34 | /24 | 192.168.10.0 | 192.168.10.255 | 254 |
| 10.20.4.77 | /20 | 10.20.0.0 | 10.20.15.255 | 4,094 |
| 172.16.9.200 | /27 | 172.16.9.192 | 172.16.9.223 | 30 |
Formula used
Network address = IP address AND subnet mask.
Broadcast address = Network address OR wildcard mask.
Wildcard mask = 255.255.255.255 minus subnet mask.
Total addresses = 2(32 − prefix).
Usable hosts = Total addresses − 2 for most subnets. For /31, both addresses are usable in point-to-point links. For /32, one host exists.
Child subnet count = 2(new prefix − base prefix).
Addresses per child subnet = 2(32 − new prefix).
How to use this calculator
- Enter a valid IPv4 address from the network you want to inspect.
- Enter a CIDR prefix, or leave it blank and provide a subnet mask.
- Add a new prefix if you want the network split into smaller subnets.
- Choose how many generated subnets should appear in the table.
- Press submit to show results above the form and below the header.
- Use the CSV or PDF buttons to export the calculated details.
Frequently asked questions
1. What does the calculator return?
It returns the network address, broadcast address, first and last usable hosts, subnet mask, wildcard mask, host counts, binary values, address class, and private or public scope.
2. Can I enter a subnet mask instead of CIDR?
Yes. If the mask is valid and contiguous, the page converts it into the matching prefix length automatically, then performs the same subnet calculations.
3. Why do usable hosts drop by two?
Most IPv4 subnets reserve one address for the network identifier and one for broadcast traffic. Those addresses cannot be assigned to normal hosts.
4. What happens with /31 and /32 networks?
A /31 can support two usable endpoints on point-to-point links. A /32 identifies one single host address, so the result shows one address.
5. What is the wildcard mask used for?
A wildcard mask is the inverse of the subnet mask. It is often used in routing, access control entries, and network policy matching.
6. Can this calculator split larger networks?
Yes. Enter a new prefix larger than the base prefix, and the tool lists child subnets up to the limit you request.
7. Does it support IPv6?
No. This version is focused on IPv4 subnetting only. IPv6 uses different addressing rules, prefixes, and planning methods.
8. Why export the results?
Exports help you document plans, share subnet breakdowns with teams, keep audit records, and attach calculations to deployment or change requests.