About the Subnet Calculator
This IPv4 subnet calculator takes a CIDR address such as 192.168.1.10/24 and computes everything you need to understand the block: the network address, broadcast address, netmask, wildcard mask, the usable host range and the total host count. It is a quick reference for planning networks, configuring firewalls or sizing a subnet.
The calculation is pure math and runs entirely in your browser — no address or network detail is sent anywhere. Use it when subnetting a VLAN, checking whether an IP falls inside a range, working out ACL wildcard masks for router configs, or teaching yourself how CIDR notation maps to address boundaries.
How to use it
- Enter an IPv4 address with a CIDR prefix, for example 10.0.0.5/22.
- Read the computed network and broadcast addresses.
- Check the netmask and its inverse wildcard mask.
- Use the usable host range and host count to plan assignments.
- Adjust the prefix length to compare how the block grows or shrinks.
Examples
- 192.168.1.10/24 -> network 192.168.1.0, broadcast 192.168.1.255, netmask 255.255.255.0, usable 192.168.1.1-192.168.1.254, 254 hosts.
- 10.0.0.0/30 -> usable range 10.0.0.1-10.0.0.2, just 2 hosts, ideal for a point-to-point link.
- 172.16.0.0/16 with wildcard mask 0.0.255.255 for an ACL rule, covering 65,534 usable hosts.
Frequently asked questions
What is a CIDR subnet calculator?
It is a tool that converts an address-plus-prefix like 192.168.1.0/24 into the network's boundaries: network and broadcast addresses, masks, host range and host count.
What is the difference between a netmask and a wildcard mask?
A netmask (e.g. 255.255.255.0) marks the network bits, while the wildcard mask is its bitwise inverse (0.0.0.255), commonly used in router ACLs and OSPF configuration.
How is the usable host count calculated?
For a standard IPv4 subnet it is 2^(32 minus prefix) minus 2, because the network and broadcast addresses are reserved. A /24 gives 254 usable hosts.
Does my input get sent to a server?
No. The subnet calculation is plain arithmetic performed entirely in your browser, so the addresses you enter never leave your device.
Can it calculate IPv6 subnets?
This tool focuses on IPv4 CIDR math. IPv6 uses a much larger 128-bit address space and different conventions, which are outside its scope.
Why do /31 and /30 networks behave differently?
A /30 has 2 usable hosts after reserving network and broadcast. A /31 is a special case (RFC 3021) used for point-to-point links where both addresses are usable.