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IPv4 Subnet Calculator

Inspect CIDR blocks, masks, usable addresses and point-to-point exceptions.

Your numbers

Make it your own
Updates as you type
IPv4 network
192.168.1.0/24

Calculated from your inputs · rounded for display

Subnet mask255.255.255.0
Address count256
Usable addresses254
Broadcast192.168.1.255
First usable192.168.1.1
Last usable192.168.1.254

/31 uses point-to-point semantics with both addresses usable (RFC 3021); /32 identifies one host. Other prefixes reserve network and broadcast addresses. IPv4 only.

Your calculation, step by step

No black boxes
  1. Address block size = 2^(32 − 24) = 256.
  2. Round the integer address down to a multiple of 256.
  3. Network = 192.168.1.0; last address = 192.168.1.255.

How to use this calculator

  1. Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
  2. Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
  3. Copy, share, save, or download your result. Saved inputs stay on this device.

How the calculation works

Address count = 2^(32 − prefix); network = floor(address / block size) × block size

An IPv4 address is a 32-bit integer shown as four octets. The prefix specifies how many leading bits define the network. Ordinary subnets reserve the first address for the network and the last for broadcast. This tool treats /31 as a point-to-point block and /32 as one host, rather than subtracting two blindly.

A worked example

192.168.1.10/24 belongs to 192.168.1.0/24, with 256 addresses and 254 ordinary usable host addresses.

Reading your result

Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.

Frequently asked questions

What happens with /31?

Both addresses are treated as usable for point-to-point links under RFC 3021.

Is IPv6 supported?

No. This tool is explicitly IPv4.

Sources & methodology

IETF RFC 3021: 31-bit prefixes on IPv4 point-to-point links ↗

Formula review: October 24, 2026. Read our methodology.