IPv4 subnet calculator

What it does

Convert CIDR prefixes and netmasks, calculate address ranges and check whether an IPv4 address belongs to a subnet.

How to use it

1. Enter a dotted IPv4 address and either a CIDR prefix such as /24 or a netmask such as 255.255.255.0.
2. Optionally enter an address to check containment in the full subnet range. Results include network, netmask, address count and usable host range.
3. /31 treats both addresses as usable for a point-to-point link; /32 represents one host. Other prefixes exclude network and broadcast addresses from usable hosts.

Example

192.168.1.10 with /24 gives network 192.168.1.0/24 and 254 conventional usable hosts.

Methodology

Unsigned 32-bit address arithmetic aligns the address to a power-of-two block. Netmasks must have contiguous leading one bits.

Limitations

IPv4 only. No network scanning, DNS lookup or reachability check. Usable counts do not account for provider reservations or routing policy.

Automation

This tool runs in your browser. No upload API or MCP endpoint is available.