How do I calculate the number of hosts from CIDR?

The number of hosts is calculated as 2^(32 - prefix_length) - 2. The -2 accounts for the network and broadcast addresses. For example, /24 gives 2^8 - 2 = 254 usable hosts.

CIDR Calculator - Free Online CIDR Notation Calculator

CIDR to IP Range Converter

ℹ How it works: Enter a CIDR notation below to see the network range, available IPs, and network details instantly.

CIDR Notation: —

Network Address: —

Subnet Mask: —

First Host: —

Last Host: —

Broadcast Address: —

Total Addresses: —

Usable Hosts: —

CIDR Notation

IP Range to CIDR Converter

ℹ How it works: Have a network IP and subnet mask? Enter both below to see the CIDR notation and complete network information.

CIDR Notation: —

Network Address: —

Subnet Mask: —

First Host: —

Last Host: —

Broadcast Address: —

Total Addresses: —

Usable Hosts: —

Network Address

Subnet Mask

Subnet Mask Calculator

ℹ How it works: Know the CIDR prefix (like /24)? Enter it below to see the subnet mask, host count, and other details.

CIDR Prefix: /24

Subnet Mask: 255.255.255.0

Wildcard Mask: 0.0.0.255

Total Addresses: 256

Usable Hosts: 254

Host Range: 254 to 256

Subnet Mask

CIDR Notation Guide

What is CIDR?

CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing Internet traffic more efficiently. It replaces the older class-based IP addressing scheme.

CIDR Notation Explained

CIDR notation consists of an IP address followed by a forward slash and a prefix length:

192.168.1.0/24

192.168.1.0 = IP Address

24 = Prefix Length (network bits)

Understanding Prefix Length

The prefix length indicates how many bits of the IP address represent the network portion. The remaining bits represent host addresses.

Example with /24:

                        Network: 192.168.1.0/24

                        First Host: 192.168.1.1

                        Last Host: 192.168.1.254

                        Broadcast: 192.168.1.255

                        Total Hosts: 254 usable (256 - 2)

Common CIDR Ranges

CIDR	Subnet Mask	Hosts
/8	255.0.0.0	16,777,214
/16	255.255.0.0	65,534
/24	255.255.255.0	254
/28	255.255.255.240	14
/32	255.255.255.255	1

Private IP Ranges

Class A Private: 10.0.0.0/8

Class B Private: 172.16.0.0/12

Class C Private: 192.168.0.0/16

Frequently Asked Questions

What is CIDR notation? −

CIDR (Classless Inter-Domain Routing) notation is a compact way to represent an IP address and its associated network mask. It's written as an IP address followed by a forward slash and a number (0-32) that represents the number of network bits. For example, 192.168.1.0/24 means the first 24 bits are the network address, and the remaining 8 bits are for host addresses.

How do I calculate the number of hosts in a network? +

The formula is: 2^(32 - prefix_length) - 2

For example, with /24: 2^(32-24) = 2^8 = 256 total addresses. Subtract 2 for the network and broadcast addresses = 254 usable hosts.

Note: For /31 and /32, the calculation is different due to point-to-point links and single hosts.

What's the difference between network and broadcast address? +

The network address is the first address in a subnet and identifies the network itself. The broadcast address is the last address in a subnet and is used to send data to all hosts in that network. Neither can be assigned to individual devices. For example, in 192.168.1.0/24, 192.168.1.0 is the network address and 192.168.1.255 is the broadcast address.

What are private IP addresses? +

Private IP addresses are reserved for use within private networks and are not routable on the public internet. The three ranges are:

• 10.0.0.0/8 (10.0.0.0 to 10.255.255.255)
• 172.16.0.0/12 (172.16.0.0 to 172.31.255.255)
• 192.168.0.0/16 (192.168.0.0 to 192.168.255.255)

These are commonly used in corporate networks and home networks.

How do I subnet a network? +

To subnet a network, increase the prefix length. For example, if you have 192.168.1.0/24, you can create two /25 subnets:

• 192.168.1.0/25 (128 addresses, 126 usable hosts)
• 192.168.1.128/25 (128 addresses, 126 usable hosts)

Use our CIDR calculator to help determine the best prefix length for your needs.

What is supernetting? +

Supernetting is the opposite of subnetting - it combines multiple smaller networks into one larger network by decreasing the prefix length. For example, combining 192.168.0.0/24 and 192.168.1.0/24 into 192.168.0.0/23. This is useful for route aggregation.

How do I validate if an IP address is valid? +

A valid IPv4 address has four octets (numbers) separated by periods, where each octet is between 0 and 255. For example:

• Valid: 192.168.1.1
• Invalid: 192.168.1.256 (256 exceeds 255)
• Invalid: 192.168.1 (missing one octet)

The CIDR calculator validates your input automatically.