Subnet Calculator - IP and CIDR

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Network Masks


Host Address Range


Reserved Addresses


Subnet Properties


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About the Online Subnet Calculator


Subnetting is a fundamental tool in any network administrator's arsenal because it allows you to logically break large networks into smaller pieces called subnets. This makes network management easier by creating segments of your network that are logically independent. A failure in one subnet can be isolated and you can create different routing and firewall rules for different subnets for better network security.

Subnetting is a way to logically separate networks into smaller, more specific segments. Each additional bit you use results in the network being split into two pieces with half as many IP addresses each. This allows you to engineer and maintain scalable and efficient networks.

This is best illustrated by an example: Suppose you have a network (this notation is called classless inter-domain routing or CIDR notation) and you would like to subdivide it. By increasing the subnet mask from 24 to 25, you split the 256 addresses in the original /24 network into two /25, each with 128 addresses.

To learn more about subnets and how you can calculate them yourself, read our detailed article on subnetting.

Online Subnet Calculator and Free API

The online subnet calculator allows you to quickly calculate the network details for an IPv4 address or CIDR block. Use this free online calculator to determine subnet mask, wildcard mask, network address, broadcast address, and assignable hosts. Use this tool as a subnet mask calculator to translate between CIDR notation and dotted-decimal notation for subnet masks.

You can view the results in two formats: dotted decimal notation and binary notation.

View the results in an editable IP address table or print the subnet details for reference. This tool has a free API that offers functionality for integrating subnet calculations into your own software projects. The calculator and its associated API are free to use and are ideal for systems administrators, network administrators, Information Technology specialists, and students.

With a NetworkCalc account, you can save the subnet, track IP address assignments, and monitor the health and status of your domain.