What a subnet mask means
A mask such as 255.255.255.0 is a 32-bit value. The 1 bits represent the network portion and the 0 bits represent the host portion.
Calculate IPv4 network, broadcast, wildcard masks, and usable host ranges from IP and CIDR.
Tip: You can also type like 10.0.1.5/20; the prefix will auto-fill.
Start with these examples
Check whether an existing network can be split into longer prefixes, and list the resulting subnets.
Subdivision examples
Validate that multiple CIDRs are non-overlapping and check if they can be subdivided to the specified prefix.
Multi-CIDR examples
Shows each input normalized to network boundary with start/end addresses.
Example of how the target CIDR is subdivided and placed between preceding and following CIDRs.
A subnet mask shows which bits of an IPv4 address belong to the network, while CIDR expresses the same boundary in a short form such as /24. This page keeps the calculator first, then adds the practical reference you usually need during design or troubleshooting.
A mask such as 255.255.255.0 is a 32-bit value. The 1 bits represent the network portion and the 0 bits represent the host portion.
/24 means the first 24 bits are the network. It is the short form of the same boundary described by 255.255.255.0.
When you look at the network address, broadcast address, and usable host count together, you can quickly judge the size and boundaries of the subnet.
These are prefixes that appear often in small LANs, VLAN splits, and point-to-point links.
| CIDR | Subnet mask | Total addresses | Usable hosts | Typical use |
|---|---|---|---|---|
| /24 | 255.255.255.0 | 256 | 254 | Typical small LAN or department segment |
| /26 | 255.255.255.192 | 64 | 62 | When one /24 needs to be split into four parts |
| /27 | 255.255.255.224 | 32 | 30 | Smaller VLANs or lab environments |
| /30 | 255.255.255.252 | 4 | 2 | Traditional point-to-point links |
| /31 | 255.255.255.254 | 2 | 2 | RFC 3021 point-to-point links |
| /32 | 255.255.255.255 | 1 | 1 | Single hosts, loopbacks, and route targets |
When you want four smaller segments from one /24, the subdivision checker shows the resulting CIDRs immediately.
Even if you enter a host address such as 192.168.10.34/27, the calculator derives the containing network and the usable host range.
Use the multi-CIDR checker to spot overlaps and gaps before you finalize an addressing plan.
They describe the same network boundary. A subnet mask uses dotted decimal notation such as 255.255.255.0, while CIDR uses a short prefix such as /24.
A /24 has 256 total addresses. In a typical IPv4 subnet, 254 are treated as usable hosts because the network and broadcast addresses are reserved.
/31 is commonly used on point-to-point links to avoid wasting addresses. /32 is used for single hosts, loopbacks, and route destinations.
Not in a normal IPv4 subnet. For example, in 192.168.0.0/24, 192.168.0.0 is the network address and 192.168.0.255 is the broadcast address. In 192.168.0.0/18, however, the broadcast address becomes 192.168.63.255, so 192.168.0.255 can be used as an address inside that larger subnet. If that /18 is later split into /24 networks, 192.168.0.255 becomes the broadcast address of 192.168.0.0/24 again. This calculator follows that rule for usable host counts, with /31 and /32 treated as special operational cases.
The docs section now includes the basics, a CIDR quick reference, and step-by-step subdivision examples.