Free web tool

SubNet Calculator

Work out networks, masks, host ranges and more from an IP address and CIDR, on your phone or desktop.

Open SubNet Calculator How to use

Version 2.1 Updated October 11, 2026 What's new

What it does

Type an IP address and pick a prefix like /24, and the SubNet Calculator gives you everything about that network at once: the network and broadcast addresses, first and last usable host, mask and wildcard, how many addresses, and whether it's private or public.

Built for setting up routers, cellular gateways and phone systems in the field: big buttons, quick prefix picks, and it works with no signal once you've opened it.

Features

  • Overview: network, broadcast, first and last host, mask, wildcard, total and usable addresses, class and private/public.
  • Binary view of the address and mask, and a bar showing network bits against host bits.
  • Divide a network into smaller subnets.
  • Same Subnet: check whether two addresses are on the same network.
  • Overlap: see whether two networks overlap.
  • Supernet: combine networks into the smallest one that covers them.
  • One-tap common prefixes, a CIDR reference table, recent history and Copy All.
  • Works offline after the first visit: everything is worked out on your device. Dark or light, sized for phones.

Screenshots

Enter an address and prefix, or tap a common one.
Enter an address and prefix, or tap a common one.
Everything about the network at once, ready to copy.
Everything about the network at once, ready to copy.

How to use

  1. Open the SubNet Calculator once while you have a signal; your phone keeps a copy.
  2. Type an IP address, pick a prefix like /24 (or tap a common one) and tap Calculate.
  3. Use the tabs for Binary, Divide, Same Subnet, Overlap and Supernet. Copy All copies every result.
  4. On Android: tap ⋮ then Add to Home screen for a one-tap icon that works with no signal.

Questions

Does it need a connection?

Only the first time. After that your phone keeps a copy and does all the math itself, so it works on a job site with no signal.

Does it do IPv6?

Not yet; it's for IPv4 networks.