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About IP Subnet Calculator Online
This tool computes subnet details from an IP address and CIDR prefix (or subnet mask). It returns the network address, broadcast address, usable host range, total number of hosts, the wildcard mask, and the CIDR notation — everything you need to plan or document a subnet.
Subnet calculations come up daily in network administration: carving up a larger network into VLANs, configuring firewall rules, planning IP allocations for a new office, troubleshooting connectivity, or computing supernet aggregates. Getting the math right by hand is error-prone; the calculator makes it instant.
Use it when sizing a new subnet, double-checking router configurations, or studying for CCNA / Network+ certifications.
How to use this tool
How to compute the network and broadcast of an IPv4 CIDR
Enter a CIDR
"IPv4 CIDR" expects the form `ip/bits` — e.g. `192.168.1.0/24` or `10.0.0.5/16`. The IP doesn't need to be the network address; the tool normalises it for you.
Range and validation
Bits must be 0–32. Each octet of the IP must be 0–255. Anything else throws "Invalid CIDR." or "Invalid IP." — there's no IPv6 support here.
Press Run
Result returns networkAddress (first IP in the block), broadcastAddress (last IP), and usableHosts (2^(32 − bits) − 2; clamped to 0 for /31 and /32).
Quick reference
/24 → 254 usable hosts; /30 → 2 (typical point-to-point link); /32 → 0 (single host); /0 → covers the entire IPv4 internet. For VLSM planning, run the tool multiple times for each subnet.