IP Subnet Calculator

How to use the calculator

1. Enter an IPv4 address in IP address, such as 192.168.1.10. You can include a CIDR suffix, such as 192.168.1.10/24; that suffix overrides the prefix or mask selected below.
2. Choose Subnet format. Select Prefix length to choose a value from /0 to /32, or Dotted subnet mask to enter a contiguous Subnet mask, such as 255.255.255.0.
3. Set Split subnet to Do not split for details about the original subnet. To divide it, select Into N equal subnets and enter Number of subnets (N), or select By new prefix length and choose New prefix length.
4. Read Subnet Details for the network, address range, masks, and host counts. If you requested a split, inspect Equal subnets for each resulting network and its host range.

What an IPv4 subnet tells you

An IPv4 address has 32 bits. A prefix length specifies how many leading bits identify the network; the remaining bits distinguish addresses within it. CIDR notation combines a network address and prefix, such as 192.168.1.0/24. A dotted subnet mask expresses the same boundary: /24 corresponds to 255.255.255.0. The wildcard mask reverses the mask’s bits, so it is 0.0.0.255 in this example.

Network address is the first address in the calculated range, and Broadcast address is the last. In an ordinary subnet from /0 through /30, the calculator excludes those two endpoints when reporting First usable host, Last usable host, and Usable hosts. Total addresses still includes both endpoints. These figures describe the size of the range, not how many devices are connected or how many addresses your network can actually assign.

IP class describes the entered address using historical classful categories. Modern subnet boundaries come from the selected prefix or mask, not the class. Address type classifies the entered IP against common private and special-use ranges; it does not classify every address in the resulting subnet. A “Public” label only means the IP did not match the common special-use ranges checked here—it does not establish that the address is assigned or reachable.

Splitting a subnet into equal parts

To make \(s\) equal subnets, where \(s\) is a power of two, add \(\log_2(s)\) bits to the original prefix. For example, splitting a /24 into four subnets produces /26 networks. Each /26 contains \(2^{32-26}=64\) total addresses and, under the usual endpoint rule, 62 usable hosts. The four networks begin at 192.168.1.0, 192.168.1.64, 192.168.1.128, and 192.168.1.192.

Alternatively, choose a longer New prefix length. The calculator determines how many equal subnets fit and lists their network address, displayed broadcast address, host range, and usable-host count. A split must fit within the original prefix and produce no more than 256 rows. When entering Number of subnets (N), use a power of two between 2 and 256.

Assumptions and practical limits

• Only IPv4 addresses and contiguous subnet masks are accepted. This calculator does not process IPv6.
• For /31, both addresses count as usable on a point-to-point link under RFC 3021. The field labeled Broadcast address still displays the higher address, but it is not a conventional broadcast address in that use. For /32, the single address counts as one usable host, and the network and displayed broadcast addresses are identical.
• Host counts are mathematical counts. Reserved ranges, routing rules, provider assignments, and local configuration may further restrict which addresses you can use.

The Binary IP and mask result makes the network-bit boundary visible; the Binary Converter can help when examining individual bit values. The Hexadecimal IP and mask result shows each 32-bit value in hexadecimal, which you can explore further with the Hex Converter.