IP Subnet Calculator

What this calculator does

The IP Subnet Calculator describes an IPv4 subnet from an address and a prefix length. Given an address such as 38.60.220.222 and a prefix such as /30, it finds the network address, the broadcast address, the first and last usable host addresses, the subnet mask, the wildcard mask, and the number of addresses in the subnet.

Subnetting divides a larger network into smaller logical networks. Routers use the network prefix to forward packets, and every host on a subnet shares that prefix. In CIDR notation, the prefix length is the number of leading network bits; the remaining bits identify hosts.

How to use this calculator

1. Enter a valid IPv4 address in dotted-decimal form, such as 192.168.1.10.
2. Choose a prefix length from 0 to 32 in the dropdown, such as /24.
3. Click Calculate.
4. Read the network address, usable host range, broadcast address, host counts, and masks.

The default example is 38.60.220.222/30. The network is 38.60.220.220, the broadcast address is 38.60.220.223, the usable range is 38.60.220.221 through 38.60.220.222, and there are four total addresses with two usable hosts.

IPv4 subnet formulas

Host bits = 32 − prefix
Total addresses = 2^host bits
Network address = IP address with all host bits set to 0
Broadcast address = IP address with all host bits set to 1
Usable hosts = total addresses − 2   (for prefixes /0 through /30)
Subnet mask = 32-bit mask with prefix ones followed by host-bit zeros
Wildcard mask = bitwise inverse of the subnet mask

The calculator uses unsigned 32-bit arithmetic. A /24 leaves eight host bits and contains 256 addresses, from .0 to .255. The network and broadcast addresses cannot be assigned to hosts.

What the results mean

The network address is the lowest address in the block and identifies the subnet itself. The broadcast address is the highest address and is used to reach every host on the subnet. The usable host range runs from the address after the network address through the address before the broadcast address.

The subnet mask shows the same prefix in dotted-decimal form. The wildcard mask is its inverse and appears in access lists and routing configurations. The IP class label groups prefixes as A up to /8, B through /16, and C beyond. Modern networks use CIDR, so the prefix is authoritative.

Assumptions and limitations

• Only IPv4 is supported. IPv6 uses a different address format and a 128-bit prefix space.
• Prefixes /31 and /32 are reported with zero usable hosts, matching the convention used by many subnet calculators. RFC 3021 permits two addresses on a /31 point-to-point link, but this calculator does not adopt that convention.
• The calculator does not determine whether an address is public, private, reserved, or routable on the Internet.
• It does not validate against live routing tables, allocate addresses, or check for overlaps between subnets.
• Leading zeros in an octet are rejected to avoid ambiguity with octal notation.

Frequently asked questions

How many hosts does a /24 subnet have?

A /24 has 256 total addresses. Subtracting the network and broadcast addresses leaves 254 usable hosts.

What is the difference between a subnet mask and a wildcard mask?

A subnet mask has ones for the network bits and zeros for the host bits. A wildcard mask is the bitwise inverse, with zeros for the network bits and ones for the host bits. Wildcard masks appear in some router and firewall configuration formats.

Why do /31 and /32 show zero usable hosts?

The usual IPv4 host-count rule subtracts two addresses for the network and broadcast. A /31 has only two addresses and a /32 has only one, so that rule leaves no assignable hosts. Point-to-point links can use RFC 3021, but this calculator follows the common conservative convention.

Reference tables

Example subnet

Address classes

Common prefixes

Source

Reference: Calculator.net — IP Subnet Calculator.

Disclaimer

This calculator provides estimates for educational and planning purposes. Always verify subnet design and address allocation against your network plan and relevant standards before deployment.