Subnet Calculator

Network address, broadcast, host range from CIDR.

Calculate the network address, broadcast address, subnet mask and usable host range from an IPv4 address and CIDR prefix.

How it works

The CIDR prefix defines how many leading bits are the network part. The tool applies that mask to your IPv4 address to find the network and broadcast addresses and the range of usable host addresses between them.

When it helps

Essential for network planning, configuring routers and firewalls, cloud VPCs, and networking certification study.

How CIDR notation works

An IPv4 address is 32 bits. The number after the slash says how many of those bits identify the network; the rest identify hosts inside it. A /24 leaves 8 host bits, giving 2⁸ = 256 addresses, while a /26 leaves 6 bits, giving 64. The subnet mask is simply those network bits written as an address — /24 is 255.255.255.0 and /26 is 255.255.255.192.

A worked example

Enter 192.168.1.130 with a prefix of /26. The mask is 255.255.255.192, so the network block runs in steps of 64: .0, .64, .128, .192. The address .130 falls in the .128 block, so the network address is 192.168.1.128 and the broadcast address is 192.168.1.191. Usable hosts run from 192.168.1.129 to 192.168.1.190 — 62 in total, because the network and broadcast addresses can't be assigned to devices.

Common prefixes at a glance

/30 gives 4 addresses (2 usable) and is a classic choice for point-to-point links. /28 gives 16 (14 usable), /27 gives 32 (30 usable), /24 gives 256 (254 usable), and /16 gives 65,536 (65,534 usable). The private ranges you'll see most often are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16.

Frequently asked questions

How many hosts are in a /24?

256 addresses, 254 of which are usable hosts.

Why subtract two addresses?

The network address and broadcast address can't be assigned to hosts in a normal subnet.

Why does a /31 show 0 usable hosts?

The tool follows the classic rule of reserving the network and broadcast addresses. In practice, RFC 3021 allows /31 networks to use both addresses on point-to-point links, and a /32 refers to a single host.

Does it support IPv6?

Not yet — the calculator works with IPv4 addresses only.

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