Subnet Calculator
IPv4 CIDR in — network, broadcast, host range and mask out. Paste 192.168.1.10/24 or a bare IP.
What the numbers mean
A CIDR block like 192.168.1.0/24 says: the first 24 bits are the network, and the
remaining 8 bits belong to the hosts. That single number decides the netmask
(255.255.255.0), how many addresses exist in the block (2⁸ = 256) and how many of
them a device can actually use. Traditionally the first address is the network itself and the
last is the broadcast — both reserved, which is why a /24 yields 254 usable hosts.
This calculator also flags whether the block is inside a private range
(10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 or
127.0.0.0/8) or routable on the public internet, and shows the wildcard mask that
firewall and ACL rules expect. Everything is computed with bit arithmetic on plain integers —
no lookups, nothing leaves your browser.
FAQ
Why does my /31 or /32 show unusual host counts?
Point-to-point /31 links have 2 usable addresses by RFC 3021 convention, and a /32 is a single host route. The calculator applies those exceptions and says so in the output.
Can I enter an IP without a prefix?
Yes — a bare address is treated as /32 and you can then click a quick CIDR button to widen it.
Does it support IPv6?
Not yet — this tool covers IPv4, which is still where subnet math bites day to day.