Why are usable hosts 2 less than the total address count?

The first address is reserved as the network address and the last as the broadcast address — neither is assignable to a device, so both are excluded.

What's a wildcard mask used for?

It's the inverse of the subnet mask, commonly used in router access control lists and some routing protocol configurations.

What's the difference between /24 and /16?

A smaller prefix number reserves fewer bits for the network and more for hosts — a /16 gives 65,534 usable addresses versus a /24's 254, at the cost of a much larger address block.

Why do /31 and /32 show no usable host range?

They reserve too few (or zero) host bits for a traditional network/broadcast split — /31 is a special case used for point-to-point links (RFC 3021) and /32 identifies a single host route.

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IP Subnet Calculator

Network address, broadcast, mask, and usable host range from a CIDR.

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About the IP Subnet Calculator

Calculates the network address, broadcast address, subnet mask, and usable host range for an IPv4 address and CIDR prefix — standard networking math used when configuring subnets.

How to use it

Enter an IP address.
Enter a Prefix length (CIDR), from 0–32.
Read the network address, subnet mask, broadcast address, and usable host range in the readout.

Formula

Subnet mask is derived from the prefix length. Network address = IP AND mask. Broadcast address = network address OR (NOT mask). Usable hosts = 2^(32−prefix) − 2.

Standard IPv4 CIDR (Classless Inter-Domain Routing) math, as specified in RFC 4632.

Worked example

192.168.1.0/24 has a network address of 192.168.1.0, a broadcast of 192.168.1.255, and 254 usable host addresses.

Recommendations

• A /24 network is a common default for small local networks, giving 254 usable addresses — smaller prefixes like /28 suit point-to-point links or small device groups.
• The network and broadcast addresses aren't assignable to devices — only the addresses between them are usable hosts.
• /31 and /32 are special cases with no traditional usable host range, often used for point-to-point links and single-host routes.

Frequently asked questions

It's the number of bits reserved for the network portion of the address — a /24 reserves 24 bits, leaving 8 bits (256 addresses) for hosts.

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Sources

RFC 4632 — Classless Inter-domain Routing (CIDR) — accessed 2026-08-20