IPv4 Subnet Calculator

How IPv4 Subnet Calculator works

Work out the network, broadcast, mask and usable hosts for a CIDR block. Essential for configuring firewalls, routers and VLANs correctly. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

What CIDR notation means

192.168.1.10/24 means the first 24 bits are the network and the last 8 identify the host. The address therefore sits in the 192.168.1.0 network, whose usable range is 192.168.1.1 to 192.168.1.254 with a broadcast at .255.

The prefix length is the whole calculation: /24 gives 256 addresses, /25 gives 128, /26 gives 64 and so on, halving each time.

Usable hosts, not total addresses

Every subnet reserves two addresses: the network address and the broadcast. A /24 has 256 addresses and 254 usable hosts. A /30 has 4 addresses and 2 usable — which is exactly what a point-to-point link needs.

A /31 is a special case defined for point-to-point links with 2 usable addresses and no broadcast, and /32 is a single host route.

Private ranges

10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are reserved for private networks and never routed on the public internet. A host on 192.168.x.x that cannot reach anything is usually a gateway or DNS problem, not a routing one.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions