IP Subnet Calculator
CIDR ranges, masks and usable hosts.
IP Subnet Calculator takes an IPv4 address with a CIDR prefix or a netmask and returns the network address, broadcast address, usable host range, host count, wildcard mask and the binary breakdown. It also splits a block into equal subnets and handles IPv6 prefixes. The arithmetic is done in your browser, with nothing looked up.
Loading IP Subnet Calculator…
Runs entirely on your device. No file or text you enter here is uploaded. How to verify it.
How to use IP Subnet Calculator
- Enter an address with a prefix, like 192.168.1.10/24.
- Read the network, broadcast, mask and host range.
- Optionally split the block into smaller subnets.
Questions about IP Subnet Calculator
Why are there two fewer usable hosts than addresses?
The first address in an IPv4 subnet is the network identifier and the last is the broadcast address, so a /24 has 256 addresses but 254 usable hosts. The exceptions are /31, used for point-to-point links, and /32, a single host.
Does it query anything on the network?
No. Subnetting is pure arithmetic on the address bits — there is nothing to look up. That is why it works offline, unlike an IP lookup, which this deliberately is not.
Does it handle IPv6?
Yes, for prefix arithmetic: network, range and address count. IPv6 has no broadcast address and subnets are conventionally /64, which the tool notes.
Does it tell me who owns an IP address?
No. There is no lookup of any kind here — the tool does arithmetic on the address bits and stops. WHOIS and geolocation need a server query, which is exactly what a page designed to work offline avoids.
Can I work out a subnet on my phone?
Yes. The page runs in a mobile browser and needs no connection once loaded, which makes it usable in a comms room or in front of a rack with no signal. Installed as an app, it is there with the network down.
Is IP Subnet Calculator really free, with no limits?
Yes. There is no account, no daily cap, no file-size tier and no watermark, because there is no server cost to recover. The site is funded by clearly disclosed partner recommendations on the Partners page, never by metering the tools.
Are my files or text uploaded when I use IP Subnet Calculator?
No. Everything is processed by JavaScript running in your browser, on your device. You can verify it: open your browser's developer tools, switch to the Network tab, and use the tool. You will see no request carrying your data — because there is nowhere for it to go.