Why subnetting still matters
Subnetting is one of the most practical networking skills you can learn. Whether you are designing a home lab, deploying cloud VMs, preparing for Cisco or CompTIA exams, or troubleshooting an office LAN, you need to understand how an IP network is divided into smaller pieces. This calculator gives you instant answers, but it also helps you build intuition for how address blocks work.
How to use this IP subnet calculator
- Enter any valid IPv4 address (for example: 10.0.5.23).
- Enter a subnet in CIDR form (/20 or 20) or mask form (255.255.240.0).
- Click Calculate Subnet to see network details instantly.
The tool returns network address, broadcast address, usable host range, host counts, binary values, and address type.
What each result means
Network address
The network address identifies the subnet itself. It is always the first address in the block and is created by applying the subnet mask to the IP address with a bitwise AND operation.
Broadcast address
The broadcast address is the final address in the subnet. In traditional IPv4 networks, packets sent to this address are delivered to every host in that subnet.
Usable host range
For most subnets, the usable range excludes the network and broadcast addresses. Special case: a /31 can be used for point-to-point links, and a /32 represents exactly one address.
Wildcard mask
The wildcard mask is the inverse of the subnet mask. It is commonly used in ACLs and route filtering rules. Example: subnet mask 255.255.255.0 has wildcard 0.0.0.255.
Common CIDR blocks at a glance
| CIDR | Subnet Mask | Total Addresses | Usable Hosts |
|---|---|---|---|
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
Practical subnetting tips
- Use larger prefixes (like /28 or /29) for tiny segments such as management interfaces or point-to-point links.
- Reserve address space for growth so you do not have to re-IP later.
- Document VLAN IDs, gateway addresses, and DHCP scopes alongside each subnet.
- Double-check overlap when adding new networks in cloud environments and VPNs.
Frequently asked questions
Can I enter subnet mask instead of CIDR?
Yes. The calculator accepts both CIDR notation and dotted-decimal masks.
Does this support IPv6?
This version is focused on IPv4 subnetting. IPv6 can be added as a separate calculator because the workflow is different.
What happens with invalid masks?
Non-contiguous masks (for example, 255.0.255.0) are rejected because they are not valid modern subnet masks.