Working out a subnet by hand means the same bit math every time: build a mask from the prefix length, AND it with the address for the network, OR it with the mask’s complement for the broadcast. Our new Subnet Calculator does that instantly, and gets the edge cases right that a lot of quick mental math (or a sloppy tool) gets wrong.
- Instant — type a CIDR block like
192.168.1.0/24and every value updates as you go: network address, broadcast address, subnet mask, wildcard mask, first and last usable host, and total address count. - /31 handled per RFC 3021 — a /31 has exactly one host bit, and the classic network+1..broadcast-1 rule would leave zero usable addresses. RFC 3021 fixed that for point-to-point links by making both addresses usable, and this tool follows that rule instead of silently returning zero.
- /32 handled as a single host — no host bits means no separate network or broadcast address, just one address, and the tool says so plainly.
- Wildcard mask included — useful for Cisco ACLs and OSPF
networkstatements, which ask for the mask’s complement rather than the ordinary subnet mask. - Private by default — every calculation runs in your browser with plain integer bit operations; nothing you type is ever sent to a server.
Try 192.168.1.0/24 for the ordinary case, or 10.0.0.0/30 to see the
smallest subnet that still gets a network and broadcast address of its
own — and if you write technical docs, the calculator is
embeddable on your own site with one
iframe.