IPv4 / CIDR Subnet Calculator & Validator
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Enter a CIDR block to get its network, broadcast, mask, and usable host range — then check which IPs fall inside it. Handles /31 and /32 correctly and flags host bits set by mistake. All in your browser, nothing uploaded.
How it works
- Enter a CIDR block to get its network and broadcast address, netmask, wildcard mask (the inverse, used in Cisco ACLs), usable host range, and address counts. Optionally paste a list of IPs to see which fall inside it.
- /31 and /32 don’t follow the usual “minus 2” rule. A /31 is a point-to-point link with 2 usable hosts (RFC 3021) — no separate network or broadcast address — and a /32 is exactly one host. Applying
2^n − 2blindly gives 0 and −1. - Host bits set by mistake are flagged, not silently fixed.
192.168.1.10/24still computes the real network (192.168.1.0/24), but you’ll see a note saying so — that input is usually a typo, and quietly normalizing it hides the mistake. - An octet with a leading zero is rejected.
010.0.0.1means 8.0.0.1 to classicinet_aton(octal) but 10.0.0.1 to most modern parsers — the same text names two different addresses, so there’s no safe guess.
IPv4 only. Runs entirely in your browser — nothing you type here is uploaded, logged, or stored.