Subnet Calculator

Subnet Calculator — IPv4 Network, Broadcast and Host Range

Enter an IP address and a CIDR prefix and get the network address, broadcast address, subnet mask, and usable host range straight away. It's a quick way to plan or check an IPv4 network without doing the binary maths by hand.

How to Calculate a Subnet

Type an IPv4 address and choose a prefix length from /0 to /32 — the page opens with 192.168.1.0 and /24. Any address inside the subnet works, so you can enter a host's own address and see which network it belongs to. The results show the network address, broadcast address, subnet mask, wildcard mask, first and last usable host, total addresses, usable hosts, the network in CIDR notation, and the address class. If the address isn't a valid IPv4 address, the tool says so.

Understanding the Results

The prefix length says how many of the 32 bits identify the network; the rest identify hosts. For 192.168.1.0/24 the mask is 255.255.255.0, the wildcard mask is 0.0.0.255, there are 256 addresses in total, and 254 are usable because the first is the network address and the last is the broadcast address: hosts run from 192.168.1.1 to 192.168.1.254. Entering 172.16.5.130 with /26 gives the network 172.16.5.128, a broadcast address of 172.16.5.191, and 62 usable hosts from 172.16.5.129 to 172.16.5.190. A /30 leaves 2 usable hosts, which suits links between two devices, and a /8 such as 10.0.0.0/8 holds 16,777,216 addresses. The tool also handles /31, where both addresses are usable, and /32, which is a single host.

The address class (A, B, C, D, or E) is worked out from the first number in the address. It's a legacy label from before CIDR and is shown for reference only. This calculator supports IPv4 — it doesn't handle IPv6 addresses.

Good Uses for This Tool

Planning a home, office, or cloud network, checking firewall and router rules, studying for networking exams, splitting an address block into smaller subnets, and working out how many hosts a prefix provides.

Is It Actually Private?

Yes. The calculation runs in your browser — the addresses you enter are never sent to a server or stored.