Subnet / CIDR Calculator
Enter an address with a prefix (192.168.1.10/24), with a mask (10.0.0.5 255.255.255.0) or an IPv6 prefix (2001:db8::1/48). The calculator shows the network, broadcast, netmask, wildcard, first and last usable host and the host count, entirely in your browser. Optionally split an IPv4 network into smaller subnets.
This tool runs in an isolated frame on tools.freetoolspro.com. Your files and inputs stay on your device, and advertising on this page cannot read them.
Formula
Netmask = the first prefix bits set to 1. Network = address AND netmask. Broadcast = network OR wildcard (the inverted mask). Total addresses = 232 − prefix for IPv4 and 2128 − prefix for IPv6. For IPv4 /0–/30, usable hosts = total − 2; /31 links use both addresses (RFC 3021); /32 is a single host.
Privacy
This is pure arithmetic in the isolated tools.freetoolspro.com frame. No address you enter is sent anywhere.
Limits
IPv6 has no broadcast address, so the “last address” is the end of the prefix. Address-type labels (private, documentation, CGNAT, ULA…) follow IANA special-purpose registries and do not reflect your own routing.
Common questions
Why does a /24 have 254 usable hosts, not 256?
The first address identifies the network and the last is the broadcast address, so 256 − 2 = 254 can be assigned to hosts.
Can I enter a subnet mask instead of a prefix?
Yes, for IPv4. Use a contiguous mask such as 255.255.254.0.
Methodology reviewed 2026-10-27. Processing details and test approach.