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IPv4 Subnet & CIDR Calculator

Q: How many usable hosts does a /24 subnet support?

A /24 subnet supports 254 usable hosts.

Q: What is CIDR notation?

It writes the mask as a prefix length, so 255.255.255.0 is /24.

Q: Why can't I use the network and broadcast addresses?

They identify the subnet itself and address all hosts on it, so they are not assigned to devices in normal subnets.

Calculate network address, broadcast address, subnet mask, wildcard mask, and usable IP range for any IPv4 address and CIDR prefix.

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IPv4 Address

CIDR Prefix (/0 - /32)

Mathematical Formula

Subnet Mask = (0xFFFFFFFF << (32 - CIDR)); Network = IP & Mask

Overview & Explanation

An IPv4 Subnet Calculator partitions IP networks into logical sub-networks, determining exact network boundaries, broadcast addresses, and host capacities.

How It Works

Convert IP address and CIDR prefix to 32-bit binary representations.
Apply Bitwise AND with subnet mask to calculate Network Address.
Apply Bitwise OR with wildcard mask to calculate Broadcast Address.

Practical Applications

Network engineering
VLSM design
Cloud VPC CIDR allocation

How a subnet is worked out

An IPv4 address has 32 bits. The prefix length, as in /26, says how many bits identify the network, and the remaining 32 - prefix bits identify hosts. A subnet holds 2^(32 - prefix) addresses, and normally 2 are reserved: the network address and the broadcast address. So usable hosts = 2^(32 - prefix) - 2.

A /24 has 256 addresses and 254 usable hosts. A /26 has a mask of 255.255.255.192 and 64 addresses per block, so 192.168.10.0/24 splits into the blocks .0, .64, .128 and .192.

Worked example

For 192.168.10.77/26, 77 falls in the block starting at 64. The network address is 192.168.10.64, the broadcast is 192.168.10.127 and the usable hosts run from .65 to .126, which is 62 addresses. A quick method is to find the block size, 256 minus the last non-255 mask octet, and see which multiple of it your address falls in.

Edge cases

A /30 gives 2 usable hosts, a classic choice for point-to-point links. A /31 can be used for point-to-point links with both addresses usable (RFC 3021), and a /32 identifies a single host.