IPv4 Subnet Calculator

Enter an IPv4 address and a CIDR prefix (or pick a subnet mask) to instantly see the network address, broadcast address, usable host range, and total hosts. A handy check while you practice subnetting for the CompTIA Network+ and A+ exams.

Current exam references: CompTIA Network+ N10-009 and A+ 220-1101 / 220-1102.

Split this network

Divide the calculated network into equal-size subnets for VLSM practice.

How to use it

  1. Type any IPv4 address (for example 192.168.1.10).
  2. Choose the CIDR prefix — the dropdown shows the matching dotted-decimal mask.
  3. Press Calculate to see the network/broadcast addresses and the usable host range.
Worked example: calculate 192.168.1.10/24

A /24 mask has 24 network bits and 8 host bits: 11111111.11111111.11111111.00000000, or 255.255.255.0.

The first three octets identify the network, so the network address is 192.168.1.0. Setting all eight host bits to 1 gives broadcast 192.168.1.255.

There are 2^8 = 256 total addresses. Removing network and broadcast leaves 254 usable hosts: 192.168.1.1 through 192.168.1.254.

Read the step-by-step subnetting guidePractice Network+ subnetting questionsUse the IPv6 subnet calculator