About this IP Subnet Calculator
Subnetting allows network administrators to break a large network into smaller, more manageable pieces. This helps improve performance and security. This calculator performs the binary math required to determine the boundaries of a subnet based on a CIDR notation.
Who this calculator is for
- Network engineers, sysadmins, and students working with IPv4 address plans.
- Anyone sizing a subnet for home labs, offices, VLANs, or cloud networks.
- Teams checking masks, broadcast addresses, and host counts before deployment.
When to use it
- Use it to find the network address, subnet mask, and usable host range for an IPv4 subnet.
- Use it when checking whether a CIDR block has enough usable hosts for a project.
- Use it before configuring routers, firewalls, DHCP scopes, or cloud network segments.
How to use this calculator
- Enter an IP Address (e.g., 192.168.1.50).
- Select the CIDR (subnet bits) from the dropdown (e.g., /24).
- The tool calculates the Network ID, Broadcast IP, Netmask, and Usable Host Range.
Key assumptions
- This calculator is for IPv4 only and expects a dotted-quad address with four octets.
- Usable-host math follows the traditional 2^(32 - CIDR) - 2 rule, so /31 and /32 show no traditional host range.
- CIDR must be an integer from 0 through 32, and each IP octet must be an integer from 0 through 255.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
1. Netmask: Derived from CIDR (e.g., /24 = 255.255.255.0).
2. Network Address: Bitwise AND of IP and Netmask.
3. Broadcast Address: Bitwise OR of Network Address and inverted Netmask.
4. Hosts: 2^(32 - CIDR) - 2.
Inputs explained
IP Address
Any valid IPv4 address within the subnet.
CIDR
Classless Inter-Domain Routing. The number of bits set to 1 in the subnet mask.
Understanding your results
The Usable IP Range is strictly between the Network Address (first IP) and Broadcast Address (last IP). These are the IPs you can assign to devices.
Example scenarios
Home Network
IP 192.168.1.1 / 24. Mask 255.255.255.0. Range 192.168.1.1 - 192.168.1.254. Hosts 254.
Point-to-Point
IP 10.0.0.1 / 30. Mask 255.255.255.252. Range 10.0.0.1 - 10.0.0.2. Hosts 2.
Key Features
- CIDR /0 to /32 support
- Binary Calculation
- Usable Host Range
Tips & Best Practices
- A /32 subnet is a single IP (Host).
- A /31 subnet is often used for point-to-point links on modern routers (2 usable IPs, no broadcast/network ID), but traditional math says 0 hosts.
- The First usable IP is usually the Gateway.
Glossary of Terms
- Subnet Mask
- A 32-bit number that masks an IP address, and divides the IP address into network address and host address.
- Broadcast Address
- The last address in a subnet, used to send data to all devices in that subnet.
- Network Address
- The first address in a subnet, used to identify the subnet itself.