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.

Does this tool support IPv6?

No — it's built specifically for IPv4 addresses and 32-bit CIDR prefixes (0–32). IPv6 uses a completely different 128-bit addressing scheme that this calculator doesn't handle.

What happens if I enter an invalid IP address or an out-of-range prefix?

The readout is replaced with an explicit "Enter a valid IPv4 address and prefix (0–32)" message rather than showing stale or partial results.

Does entering an octet with a leading zero, like 192.168.01.1, cause an error?

No — it's parsed as the plain decimal value 1, so 192.168.01.1 and 192.168.1.1 are treated identically. This tool doesn't flag leading zeros as invalid the way some stricter IP parsers do.

What's the largest network this tool can calculate?

A /0 prefix, which spans the entire IPv4 address space — 4,294,967,296 total addresses. It's a valid input here, though it has no practical use outside of routing-table defaults and academic examples.

IP Subnet Calculator

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.

100% Free Runs in Your Browser No Sign-Up Required

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.

Common IPv4 CIDR prefixes (RFC 4632)

Common IPv4 CIDR prefixes (RFC 4632)
CIDR	Subnet mask	Usable hosts
/24	255.255.255.0	254
/25	255.255.255.128	126
/26	255.255.255.192	62
/27	255.255.255.224	30
/28	255.255.255.240	14
/29	255.255.255.248	6
/30	255.255.255.252	2

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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