What does the prefix length (like /24) actually mean?

It specifies how many bits of the address are the network portion — a /24 means 24 bits network, 8 bits for host addresses, giving 256 total addresses in that block.

Why is the usable host range smaller than the total block size?

The first address is reserved as the network address and the last as the broadcast address, so both are excluded from the usable host range.

Does it work for both IPv4 subnetting?

Yes, it's built for standard IPv4 CIDR calculations, the most common networking context where this comes up.

Does CIDR / Subnet Calculator upload my files to a server?

No. CIDR / Subnet Calculator runs entirely in your browser using on-device processing, your files never leave your device.

CIDR / Subnet Calculator

Calculate network address, broadcast address and usable host range for a CIDR block.

Runs in your browser

CIDR notation

Network address192.168.1.0

Broadcast address192.168.1.255

Subnet mask255.255.255.0

First usable host192.168.1.1

Last usable host192.168.1.254

Total addresses256

Usable hosts254

About this tool

Working with CIDR notation means calculating the network address, broadcast address, and usable host range from the prefix length, which is straightforward binary math that's still easy to miscalculate by hand, especially for less common prefix lengths. This tool calculates the network address, broadcast address and usable host range for a CIDR block, handling the binary math instantly instead of manual calculation.

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