Our free subnet calculator lets you quickly compute network details from any IP address and CIDR prefix length. Enter an IPv4 address with a subnet mask or CIDR notation to instantly see the network address, broadcast address, host range, wildcard mask, and total usable hosts. Whether you’re planning a network, configuring firewall rules, or studying for a certification, this subnet calculator provides all the details you need.

What Is a Subnet?

A subnet (subnetwork) is a logical subdivision of an IP network. Subnetting divides a network into smaller, more efficient segments. Each subnet operates as a separate network, which helps manage traffic, improve security, and optimize IP address allocation. For example, a company might use one subnet for its engineering team and another for HR, isolating traffic between departments. A subnet range calculator helps you determine the correct size and boundaries for each of these segments.

Understanding CIDR Notation

CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length, written as 192.168.1.0/24. The number after the slash indicates how many bits of the address identify the network. A /24 means the first 24 bits are the network portion, leaving 8 bits (256 addresses) for hosts. CIDR was formally defined in RFC 4632 and replaced the older classful addressing system (Class A, B, C), allowing for more flexible allocation of IP space.

Key Subnet Terms

Network Address — The first address in a subnet, identifying the network itself. It cannot be assigned to a host.

Broadcast Address — The last address in a subnet, used to send data to all hosts on the network.

Subnet Mask — A 32-bit number that separates the network portion from the host portion. For example, 255.255.255.0 means the first three octets are the network. How subnet mask is calculated can be easily verified using our tool.

Wildcard Mask — The inverse of a subnet mask, commonly used in access control lists (ACLs) and routing configurations. For a /24, the wildcard mask is 0.0.0.255.

Common Subnet Sizes

The table below shows frequently used prefix lengths and their corresponding host counts. Use our subnet calculator to verify these values for any address:

/32 — 1 address (single host, used for loopback or host routes)
/31 — 2 addresses (point-to-point links, per RFC 3021)
/30 — 4 addresses, 2 usable (smallest traditional subnet for two devices)
/24 — 256 addresses, 254 usable (the most common LAN subnet)
/16 — 65,536 addresses (typical for larger campus networks)
/8 — 16.7 million addresses (reserved for major allocations)

How to Use This Subnet Calculator

Enter any IPv4 address along with a prefix length (e.g., 10.0.0.0/22) or a dotted-decimal subnet mask (e.g., 255.255.252.0). You can calculate the subnet mask from an IP address easily using this tool.

Practical Subnetting Examples

A small office with 50 devices needs at least a /26 subnet (62 usable hosts). A point-to-point link between two routers only requires a /30 or /31. A datacenter floor with 500 servers would need a /23 (510 usable hosts) or larger. Choosing the right subnet size avoids wasting IP addresses while leaving room for growth. Run each scenario through the subnet calculator to confirm the network boundaries before applying changes. This can also help verify how to calculate subnets for real-world applications.

Variable Length Subnet Masking (VLSM)

VLSM allows a network to be divided into subnets of different sizes. Instead of using a single subnet mask across the entire network, administrators can assign /30 subnets to point-to-point links and /24 subnets to user LANs within the same address space. This maximizes address efficiency and is standard practice in modern network design. With IP subnetting calculator tools like ours, the process becomes simpler

Supernetting (Aggregation)

While subnetting divides networks into smaller pieces, supernetting combines multiple contiguous subnets into a larger block. This is also called route aggregation or summarization. For example, four /24 networks (10.0.0.0/24 through 10.0.3.0/24) can be summarized as a single /22 (10.0.0.0/22). Supernetting reduces the size of routing tables and improves router performance. The IANA IPv4 Address Space Registry shows how the global address space is allocated across regional registries using these same aggregation principles.

Related Tools

Need to convert an IP between formats? Use our IP Address Converter for decimal, binary, hex, and octal conversions. To find the hostname associated with an IP, try our Reverse DNS Lookup tool.

Subnet Calculator