IP Subnet Calculator

Calculate IP subnet details free online from any IP address and CIDR notation. Get network address, broadcast address, usable host range, and subnet mask instantly.

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How to Use This Tool

Enter an IP and CIDRAdd an IP address and the subnet size (e.g. /24)

Click CalculatePure binary arithmetic computes all subnet boundaries

Read the resultsGet network, broadcast, usable range, and total host count

Subnetting Is Binary Arithmetic, Not Guesswork

Every subnet calculation comes down to applying a bitmask to a 32-bit number and reading off specific boundary values -- the network address, the broadcast address, and the usable range in between. Doing this by hand for anything beyond simple /24 or /16 subnets gets error-prone quickly, especially for subnets that don't fall on clean byte boundaries.

This calculator performs that binary arithmetic directly: converting the IP to its 32-bit integer representation, applying the CIDR mask, and computing every relevant boundary value precisely.

Why Address Planning Still Matters in 2026

Even with IPv6 adoption growing, private IPv4 ranges remain heavily used inside corporate networks, VPN configurations, cloud VPC setups, and home networks. Properly sized subnets prevent address waste and make network segmentation -- isolating departments, IoT devices, or guest networks from sensitive systems -- straightforward to configure correctly.

Common Subnet Sizes and Their Practical Use

A /24 (254 usable hosts) suits a typical office floor or department. A /28 (14 usable hosts) suits a small server rack or point-to-point link group. A /30 (2 usable hosts) is the standard for a router-to-router link, since exactly two devices need addresses. Picking the right size avoids both waste and the need to re-architect later when a too-small subnet runs out of room.

Frequently Asked Questions

The number after the slash indicates how many bits of the 32-bit IP address are fixed as the network portion, with the remaining bits available for host addresses. A /24 means 24 bits are network, leaving 8 bits (256 addresses, 254 usable) for hosts -- the most common subnet size for small office or home networks.

The first address in any subnet is reserved as the network address (identifying the subnet itself), and the last address is reserved as the broadcast address (used to send to every host on that subnet). Neither can be assigned to an individual device, which is why a /24 subnet with 256 total addresses has only 254 usable host addresses.

Network engineers subdivide larger address blocks into smaller subnets to organize traffic, isolate departments, or efficiently allocate limited address space. A /24 wastes addresses if you only need 10 hosts; a properly sized subnet like /28 (14 usable hosts) avoids that waste while still leaving room to grow.

A subnet mask is the same information as CIDR notation, expressed differently -- as four octets like 255.255.255.0 instead of /24. Both represent exactly the same network/host boundary; CIDR notation is more compact, while the dotted-decimal mask format is what some older systems and configuration interfaces still expect.

This calculator focuses on IPv4, which still uses CIDR-based subnetting extensively in private networks, VPNs, and firewall configuration. IPv6 subnetting follows similar logical principles but uses a much larger address space with different conventions.