Subnet Calculator — Free IPv4 CIDR & Netmask Tool

IP address

Enter a prefix from 0 to 32, or type a full netmask like 255.255.255.0 in the box on the right.

About the Subnet Calculator

Working out the boundaries of an IPv4 network by hand means converting addresses to binary and lining up the mask bit by bit — easy to get wrong. This tool does the math for you: give it an address and a prefix (or a full subnet mask) and it returns the network address, broadcast address, the first and last usable host, the matching subnet and wildcard masks, how many addresses the block holds, and which classic address class it falls into. Handy for planning networks, splitting an office into smaller segments, configuring routers and firewalls, or just checking your work.

A larger prefix number means a smaller network — /30 gives you 2 usable hosts, /24 gives you 254.

The network address and broadcast address are reserved, so they can't be assigned to a device.

Not sure of the prefix? Type a full netmask like 255.255.255.192 and it's converted for you.

How it works

Three steps. No sign-up, no upload, no wait.

Enter an address

Type an IP address and pick a prefix, like 192.168.1.10 / 24.

Read the results

See the network, broadcast, host range, and mask update instantly.

Copy what you need

Grab the full summary or any single value with one click.

🔒

Private by design.Everything happens right here in your browser. Your files are never uploaded — we never see them.

Frequently Asked Questions

What is CIDR notation? ▼

CIDR (Classless Inter-Domain Routing) writes a network as an address followed by a slash and a number, like 192.168.1.0/24. The number after the slash — the prefix length — is how many bits at the start of the address are fixed for the network. A bigger number means a smaller network with fewer addresses.

What is a subnet mask? ▼

A subnet mask marks which part of an address is the network and which part identifies the individual device. It looks like an IP address — for example 255.255.255.0 — where the 255 parts are the network and the 0 parts are free for hosts. Every CIDR prefix has one matching subnet mask.

What's the difference between total and usable hosts? ▼

Total hosts is every address in the block. Two of those are reserved: the first is the network address (the name of the block) and the last is the broadcast address (used to reach everything at once). Usable hosts is what's left for real devices — total minus 2 — for prefixes up to /30.

What does a /24 network give me? ▼

A /24 fixes the first 24 bits, leaving 8 bits for hosts. That's 256 total addresses (2⁸) and 254 usable ones after the network and broadcast addresses are set aside. Its mask is 255.255.255.0 — the classic size for a home or small-office network.

How do /31 and /32 networks work? ▼

They're special cases. A /32 is a single address — one host, no network or broadcast reserved. A /31 holds just two addresses and is used for point-to-point links, where both addresses are usable and none are reserved.

Is my IP address information sent anywhere? ▼

No. Every calculation runs locally in your browser using plain arithmetic. Nothing you type is uploaded, logged, or sent over the network.