The IP Subnet Calculator computes all the details of an IPv4 subnet: network address, broadcast address, first and last usable host, subnet mask, CIDR notation, number of usable hosts, and IP class — from any IP address and subnet mask or CIDR prefix.

How to Use This Calculator

1. Enter an IP Address in dotted-decimal format (e.g., 192.168.1.0).
2. Select the CIDR Prefix from the dropdown (e.g., /24 for a Class C network), or type the subnet mask directly.
3. Click Calculate.

CIDR Notation Reference

• /8 — Class A | 255.0.0.0 | 16,777,214 usable hosts
• /16 — Class B | 255.255.0.0 | 65,534 usable hosts
• /24 — Class C | 255.255.255.0 | 254 usable hosts
• /28 — Small LAN | 255.255.255.240 | 14 usable hosts
• /30 — Point-to-point link | 255.255.255.252 | 2 usable hosts
• /32 — Single host | 255.255.255.255 | 1 address (no broadcast)

Key Concepts

Network address: First address in the subnet — identifies the network itself. Not assignable to a host.

Broadcast address: Last address in the subnet — packets sent here are delivered to all hosts. Not assignable.

Usable hosts: Total addresses minus 2 (network + broadcast), except for /31 and /32 which are special cases.

CIDR (Classless Inter-Domain Routing): The /n notation indicates how many leading bits of the address are the network portion.

Frequently Asked Questions

What is a private IP range?

RFC 1918 defines three private ranges not routable on the public internet: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Home routers typically use 192.168.0.0/24 or 192.168.1.0/24.

What is subnetting used for?

Subnetting divides a large network into smaller, more manageable segments. Benefits include reduced broadcast traffic, improved security (isolate departments), and more efficient IP address utilization.