IP Subnet Calculator

Examples

10.0.0.0/8 172.16.0.0/12 192.168.1.0/24 192.168.1.128/25 10.10.10.0/28 203.0.113.0/30 0.0.0.0/0 192.168.0.1/32
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What is IP Subnet Calculator?

IP Subnet Calculator computes network address, broadcast address, usable host range, number of hosts, subnet mask, wildcard mask, and binary representation for any IPv4 address and CIDR prefix length. It also lists all subnets when you subdivide a network, and supports supernetting (combining multiple networks into one).

Subnetting divides an IP address space into smaller segments for network design, security (isolating VLANs), and routing efficiency. The CIDR notation 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits (256 addresses) for hosts — minus the network address and broadcast address, leaving 254 usable hosts.

Common prefix lengths and their host counts: /24 = 254 hosts (class C equivalent), /16 = 65,534 hosts (class B equivalent), /8 = 16,777,214 hosts (class A equivalent), /30 = 2 hosts (point-to-point links), /32 = 1 host (a single host route). Cloud networking (AWS VPC, GCP VPC, Azure VNet) uses CIDR extensively for subnet allocation — misunderstanding CIDR leads to overlapping address spaces and routing failures.

How to Use

  1. Enter an IP address and CIDR prefix (e.g., 192.168.1.100/24) in the input field.
  2. Read the network address (first address in the block), broadcast address (last), and usable range.
  3. Check the host count to verify the subnet is large enough for your needs.
  4. Use the subnet divider to split the network into equal-sized subnets (enter the new prefix length).
  5. Use the supernet tool to find the smallest block that contains multiple networks.

Examples

192.168.1.0/24

Result: Network: 192.168.1.0 / Broadcast: 192.168.1.255 / Hosts: 192.168.1.1–192.168.1.254 / 254 usable hosts

10.0.0.0/16 subdivided into /24 subnets

Result: 256 subnets: 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, ..., 10.0.255.0/24

172.16.5.50/30 (point-to-point link)

Result: Network: 172.16.5.48 / Broadcast: 172.16.5.51 / Hosts: 172.16.5.49 and 172.16.5.50 / 2 usable hosts

Frequently Asked Questions

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length (e.g., 10.0.0.0/8). The prefix length specifies how many bits are the network portion. 2^(32-prefix) is the total address space; subtract 2 for the network and broadcast addresses to get usable hosts.

What is the difference between network address and host address?

The network address (first in the block, all host bits 0) identifies the subnet and cannot be assigned to a host. The broadcast address (last in the block, all host bits 1) is used for subnet-wide broadcasts and also cannot be assigned to a host. All addresses between them are usable.

Why does /30 only give 2 usable hosts?

/30 has 4 total addresses (2^2). Subtract the network address and broadcast address and 2 usable addresses remain. /30 is the standard choice for point-to-point router links where exactly 2 IP addresses are needed.

What are the private IP ranges?

RFC 1918 private ranges: 10.0.0.0/8 (10 million+ addresses), 172.16.0.0/12 (1 million+ addresses), 192.168.0.0/16 (65,536 addresses). These are not routable on the public internet. Use them for internal networks, VPCs, and home networks.

How do I avoid overlapping subnets in a VPC?

Plan your address space from the top down. Assign the largest block first (e.g., 10.0.0.0/16 for the VPC), then divide it into non-overlapping subnets. Use this calculator to verify that no two subnets share any addresses — a 10.0.1.0/24 and 10.0.1.128/25 overlap because 10.0.1.128/25 is contained within 10.0.1.0/24.

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