CIDR Calculator — Subnet Mask & Host Counts (IPv4 + IPv6)

How to use

Enter CIDR notation (e.g. 192.168.0.0/24) to compute the network address, broadcast, subnet mask, host counts, and first/last usable host. IPv6 prefixes are supported as well.

1. Type a CIDR in the input box (e.g. 10.0.0.0/16 or 2001:db8::/32).
2. Press "Submit" to display the result card.
3. Read the network address, broadcast, subnet mask, wildcard mask, prefix length, and host counts.
4. Use the first / last usable host values to plan DHCP pools or write firewall rules.

For IPv4, very small prefixes (/31, /32) follow special host-counting rules (point-to-point or single host). IPv6 has no broadcast address — only network and prefix length.