Free tool · 🧩 IP subnet calculator
Subnet maths,instantly.
Network, broadcast, first/last host, wildcard mask, binary view and one-click subnet splits — the calculator we hand to every NOC trainee.
Pure JavaScript — nothing is sent to a server. Practise until you can do /26 in your head.
What it checks
Everything we would look at first on a client call.
Free, no sign-up, no email gate. If the report shows red, the fix is written next to it — and we are one click away if you would rather we did it.
- Network and broadcast addresses, usable host range and count
- Subnet and wildcard masks in dotted and binary form
- Address class and whether the range is private (RFC 1918), loopback, link-local or public
- Splits into /n+1 … /n+4 with the resulting network list
FAQ
Common questions
Why are usable hosts = total − 2?
The first address identifies the network and the last is broadcast. /31 (point-to-point) and /32 (single host) are the exceptions.
What is a wildcard mask?
The inverse of the subnet mask, used in Cisco ACLs and OSPF statements: /24 → 0.0.0.255.
Does this do IPv6?
Not yet — IPv6 is on the list. Tell us if you need it.