IP Subnet Calculator
Calculate network addresses, broadcast addresses, and usable host ranges
How to Use This IP Subnet Calculator
- Enter an IPv4 address in dotted decimal format (e.g., 192.168.1.100)
- Select the CIDR notation (subnet mask) from the dropdown - this determines network size
- Click 'Calculate Subnet' to see network address, broadcast address, and host range
- Review the detailed results including binary representations and IP classification
Example: For 192.168.1.100/24: Network address is 192.168.1.0, broadcast is 192.168.1.255, usable hosts are 192.168.1.1 through 192.168.1.254 (254 addresses). The /24 mask means 256 total addresses minus network and broadcast.
Tip: Remember: usable hosts = 2^(32-CIDR) - 2. The minus 2 accounts for network address (all zeros) and broadcast address (all ones).
Why Use a IP Subnet Calculator?
Subnetting is essential for network design, security segmentation, and efficient IP address allocation in any organization.
- Designing network architecture for a new office or data center
- Segmenting networks for security (separating guest WiFi from corporate)
- Planning IP address allocation for cloud infrastructure
- Configuring firewalls and access control lists (ACLs)
- Troubleshooting network connectivity issues
- Studying for networking certifications (CCNA, Network+, etc.)
Understanding Your Results
The calculator provides all the information needed to configure network devices and plan IP address schemes.
| Result | Meaning | Action |
|---|---|---|
| /24 to /32 | Small subnets (256 to 1 hosts) | Typical for end-user networks, point-to-point links (/30, /31), and single hosts (/32). |
| /16 to /23 | Medium subnets (512 to 65K hosts) | Used for department networks, campus segments, or medium-sized organizations. |
| /8 to /15 | Large subnets (65K+ hosts) | Enterprise-scale networks. Consider further subnetting for manageability. |
| Private vs Public | RFC 1918 ranges | 10.x.x.x, 172.16-31.x.x, 192.168.x.x are private. Use NAT to reach internet. |
Meaning: Small subnets (256 to 1 hosts)
Action: Typical for end-user networks, point-to-point links (/30, /31), and single hosts (/32).
Meaning: Medium subnets (512 to 65K hosts)
Action: Used for department networks, campus segments, or medium-sized organizations.
Meaning: Large subnets (65K+ hosts)
Action: Enterprise-scale networks. Consider further subnetting for manageability.
Meaning: RFC 1918 ranges
Action: 10.x.x.x, 172.16-31.x.x, 192.168.x.x are private. Use NAT to reach internet.
Note: For /31 and /32 subnets, the traditional 'minus 2' rule doesn't apply - these are used for point-to-point links and single hosts.
About IP Subnet Calculator
Formula
Usable Hosts = 2^(32-CIDR) - 2 The CIDR number represents network bits. Subtracting from 32 gives host bits. 2^host_bits gives total addresses. Minus 2 removes network address (first) and broadcast address (last).
Current Standards: IPv4 addressing defined in RFC 791. Private address ranges in RFC 1918. CIDR notation in RFC 4632. Variable Length Subnet Masking (VLSM) allows mixing subnet sizes within an organization.
Frequently Asked Questions
What's the difference between subnet mask and CIDR notation?
They express the same information differently. A /24 CIDR equals subnet mask 255.255.255.0. The CIDR number counts the consecutive 1-bits in the binary subnet mask. /24 means 24 ones followed by 8 zeros: 11111111.11111111.11111111.00000000 = 255.255.255.0.
Why can't I use the network or broadcast address for hosts?
The network address (all host bits = 0) identifies the network itself and is used in routing tables. The broadcast address (all host bits = 1) is used to send packets to all hosts on the subnet simultaneously. Assigning either to a host would cause routing conflicts and break network functionality.
What subnet size should I use for a network with 50 hosts?
Use /26 (64 addresses, 62 usable). The next smaller /27 only provides 30 usable hosts - not enough. Always leave room for growth. If you might expand to 100 hosts, consider /25 (126 usable). Never subnet exactly to current needs.
What is a wildcard mask and when do I use it?
A wildcard mask is the inverse of a subnet mask - where subnet has 1s, wildcard has 0s. For /24 (255.255.255.0), the wildcard is 0.0.0.255. Cisco ACLs and some other network devices use wildcard masks to match IP ranges. The wildcard mask indicates which bits must match (0) and which are ignored (1).
How do I subnet a /24 into smaller networks?
To split a /24 (256 addresses) into equal subnets: /25 creates 2 subnets with 126 hosts each, /26 creates 4 subnets with 62 hosts each, /27 creates 8 subnets with 30 hosts each, /28 creates 16 subnets with 14 hosts each. Each additional bit doubles the subnets and halves the hosts.