IP Subnet Calculator

Enter an address in CIDR notation and get the full breakdown — network address, broadcast, usable host range, subnet mask, wildcard mask, binary, class, and whether it's private or public. The one tool that shows up in basically every networking job at some point, from configuring a VLAN to double-checking an ACL before you push it.

The mechanics, briefly

An IPv4 address is 32 bits across four octets. The subnet mask decides where the split falls between "network" and "host." /24 means the first 24 bits identify the network, leaving 8 bits — 256 addresses — for hosts, with 254 of those actually usable once you subtract the network address and the broadcast address at the top and bottom of the range.

Sizes worth recognising instantly

• /24 — 254 usable — the standard small office or LAN segment
• /23 — 510 usable — a medium office
• /22 — 1,022 usable — campus scale
• /16 — 65,534 usable — a full legacy Class B network
• /30 — 2 usable — the go-to for point-to-point WAN links
• /32 — a single host, used for loopbacks and static routes

Private ranges (RFC 1918)

• 10.0.0.0/8 — 16.7 million addresses, large enterprise scale
• 172.16.0.0/12 — just over a million addresses, mid-size networks
• 192.168.0.0/16 — 65,536 addresses, home and small office — the one almost everyone recognises on sight

Two questions that come up constantly

What's a wildcard mask? It's the inverse of the subnet mask, used specifically in Cisco ACLs — for /24 (255.255.255.0), the wildcard is 0.0.0.255. How many hosts does a /25 give me? 128 addresses total, 126 usable — a detail worth having memorised if you're splitting a /24 in half for two VLANs.