IP Subnet Calculator

The IP Subnet Calculator computes all critical network parameters from a single IPv4 address and CIDR prefix length: network address, broadcast address, subnet mask, wildcard mask, host IP range, and the total number of usable hosts. Whether you are a network engineer designing VLAN segmentation, a system administrator allocating IP address space, or a student studying for CompTIA Network+ or Cisco CCNA, this tool delivers instant results.

Subnetting is the practice of dividing a large IP address block into smaller sub-networks. A home router creates one subnet (typically 192.168.1.0/24). An enterprise network may have hundreds of subnets isolating servers, workstations, IoT devices, and guest WiFi. Understanding CIDR (Classless Inter-Domain Routing) notation is fundamental to modern network design.

Enter any IPv4 address and CIDR prefix (e.g., 192.168.10.50/26) and the calculator instantly returns all subnet parameters, saving minutes of manual binary arithmetic.

💡 Quick Reference: The most common subnet is /24 (255.255.255.0) with 254 usable hosts. Point-to-point WAN links use /30 (4 IPs, 2 usable). Default routes use /0.

IPv4 subnetting uses binary bitwise operations. Here are the core calculations:

Subnet Mask from CIDR Prefix

Network Address

Broadcast Address

Variable Definitions

• IP Address: The host's IPv4 address in dotted-decimal (e.g., 192.168.10.50).
• CIDR Prefix (n): Number of network bits (0–32). Determines the subnet size.
• Subnet Mask: 32-bit mask with n leading 1s. Used to identify the network portion.
• Network Address: First IP in the subnet (all host bits = 0). Identifies the subnet.
• Broadcast Address: Last IP in the subnet (all host bits = 1). Delivers packets to all hosts.
• Host Range: Network address + 1 to Broadcast address − 1.
• Usable Hosts: 2^(32 − n) − 2 (subtracting network and broadcast addresses).
• Wildcard Mask: Inverse of subnet mask. Used in Cisco ACLs and OSPF configurations.

1. Write the IP address in binary. Each octet is 8 bits. Example: 192.168.10.50 = 11000000.10101000.00001010.00110010
2. Create the subnet mask from the prefix. Write the prefix-length count of 1s, then fill with 0s. For /26: 11111111.11111111.11111111.11000000 = 255.255.255.192
3. AND the IP with the subnet mask to get the network address. 11000000.10101000.00001010.00110010 AND 11111111.11111111.11111111.11000000 = 11000000.10101000.00001010.00000000 = 192.168.10.0
4. Calculate the wildcard mask. Invert each bit of the subnet mask. 255.255.255.192 → 0.0.0.63
5. Find the broadcast address. OR the network address with the wildcard mask. 192.168.10.0 OR 0.0.0.63 = 192.168.10.63
6. Determine the host range. First host: 192.168.10.1 (network + 1). Last host: 192.168.10.62 (broadcast − 1).
7. Count usable hosts. 2^(32 − 26) − 2 = 2^6 − 2 = 64 − 2 = 62 usable hosts.

Example 1: Standard Home Network (192.168.1.100/24)

Example 2: Point-to-Point WAN Link (10.0.0.5/30)

Example 3: Enterprise VLAN (172.16.5.0/22)

Example 4: AWS VPC Subnet (10.0.1.0/26)

Example 5: Splitting a /24 into Four /26 Subnets

• •Use private RFC 1918 ranges internally: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are non-routable on the internet. Use these for all internal networks to conserve public IP space.
• •Standardize on power-of-two prefixes: Using consistent prefix lengths (/24, /26, /28) across your network simplifies documentation, training, and troubleshooting.
• •Document your IP address plan: Maintain a spreadsheet or IPAM tool with every subnet, its purpose, assigned hosts, and gateway IP. Networks become unmaintainable without documentation.
• •Reserve IPs for infrastructure: By convention, assign the first few IPs (.1, .2, .3) to routers/gateways and the last few (.254, .253) to management interfaces. This makes network documentation predictable.
• •Practice binary subnetting for certifications: While this calculator handles the math, understanding binary subnetting is required for CCNA/CCNP exams. Practice converting between decimal and binary to build fluency.

IP subnetting is a foundational networking skill that underpins everything from home routers to massive cloud data centers. Understanding how CIDR notation divides IP address space, how subnet masks define network boundaries, and how to calculate host ranges enables you to design secure, efficient networks that scale.

Use this IP Subnet Calculator to instantly compute any subnet's parameters — eliminating manual binary arithmetic and reducing configuration errors. Whether planning a small office VLAN, sizing a cloud VPC, or studying for a Cisco CCNA exam, accurate subnetting is essential. Pair this tool with the Bandwidth Calculator to also assess the throughput capacity of your network links.

🌐 Pro Tip: For IPv6 subnetting, the same principles apply but with 128-bit addresses divided by 64-bit network prefixes. Most IPv6 deployments use /64 prefix lengths for individual subnets, providing 2^64 (18 quintillion) host addresses per subnet.