Free Subnet Calculator

Subnetting is the practice of splitting one large IP network into several smaller, logical networks called subnets. These smaller sections are easier to control, more secure, and more efficient to use. While subnetting was first introduced to help deal with the limited number of IPv4 addresses, it is now a core best practice for smart IP address management and network design.

In IPv4, networks are traditionally grouped into classes such as Class A, B, and C. If you used each class as a single, flat network, you’d waste a lot of address space and create a network that’s hard to manage. Subnetting solves this by taking bits from the host portion of an IP address and using them to create multiple smaller networks inside the original one.

Each subnet contains a group of IP addresses that share the same routing prefix. Together, these subnets form a structured network made up of many interconnected segments. This structure helps you spread out traffic, reduce congestion, and keep different parts of the network logically separated.

For large organizations, subnetting is essential. Relying on a single, huge subnet would quickly become unmanageable and could cause several issues, such as:

Extra broadcast traffic is slowing down the network

Security risks from mixing sensitive and non-sensitive devices on the same subnet

A confusing, hard-to-maintain network layout

By designing and using subnets, network administrators can create cleaner, safer, and more efficient networks that are easier to scale and troubleshoot.

A subnet mask is a 32-bit number in IPv4 that splits an IP address into two parts:

the network part (which network it belongs to)

the host part (which device on that network it is)

This split helps routers send traffic to the right place and lets you organize and secure your network.

For example, take this IP address and subnet mask:

IP address: 192.168.1.10

Subnet mask: 255.255.255.0

Here, the first three numbers (192.168.1) identify the network, and the last number (.10) identifies the device on that network. So 192.168.1.10 is the host number 10 on the 192.168.1.0 network.

Subnet masks are essential because they:

Tell routers where to send packets

Help you break a big network into smaller segments for better performance

Improve security by separating different groups of devices

Reduce IP conflicts by giving each device a clear place in the network

You’ll often see subnet masks written in CIDR notation, such as /24. A “/24” means 24 bits are used for the network part, which is the same as the subnet mask 255.255.255.0.

A supernet calculator is an IP address calculator that works oppositely to a subnet calculator. Instead of breaking one network into many smaller parts, it helps you combine multiple IP networks or subnets into a single, larger “supernet.” A supernet, or supernetwork, is created when two or more compatible networks are merged and represented by one CIDR prefix. This larger block has a common routing prefix that covers all the included networks and is the same length or shorter than the smallest network prefix in the group. This process, known as supernetting or route aggregation, was introduced to reduce the size of routing tables and slow down IPv4 address exhaustion. By advertising one larger route instead of many smaller ones, routers have fewer entries to process, which means lower CPU load, less memory usage, and faster decisions. A supernet calculator makes this work simple by taking multiple IP ranges as input, checking which ones can be aggregated, and then calculating the smallest valid supernet that includes them. It outputs the summarized supernet in CIDR notation and filters out any invalid or non-matching networks. It helps network engineers and administrators design cleaner routing, simplify configuration, and optimize IP address management in a clear, accurate, and time-saving way.