IP & Subnet Calculator
Calculate network, broadcast, host range and mask from an IPv4 or IPv6 CIDR block.
Runs in your browser using BigInt address arithmetic — nothing is uploaded
How to use it
- Type an address with a prefix, such as 192.168.1.10/24 or 2001:db8::1/64.
- IPv4 and IPv6 are detected automatically; a bare address defaults to /32 or /128.
- Everything is recalculated as you type. Click any value to copy it.
Questions
Why does a /24 have 254 usable hosts and not 256?
In IPv4 the first address of a block is the network identifier and the last is the broadcast address, so neither can be assigned to a host. A /24 holds 256 addresses and 254 usable ones.
What about /31 and /32?
A /32 is a single address — one host, no network or broadcast. A /31 is the special case in RFC 3021: on a point-to-point link both addresses are usable, so it gives two hosts rather than none.
Why does IPv6 have no broadcast address?
IPv6 removed broadcast entirely in favour of multicast, so every address in a prefix is usable. The subnet-router anycast address at the start of a prefix is reserved by convention rather than by arithmetic.
Does it look anything up on the internet?
No. Every figure is arithmetic done in your browser. The tool makes no network requests of any kind, and deliberately offers no lookup, geolocation or ownership information.