CIDR Network Calculator (IPv4)
Enter an IPv4 address with prefix length to calculate subnet mask, network address, broadcast address, host range, and more.
What is a network calculator CIDR tool?
A network calculator CIDR tool converts an IP address and prefix length into practical subnet information. If you have ever seen something like 192.168.10.34/27 and needed to know the network range, broadcast address, or usable host count, this is exactly what the calculator is for.
CIDR stands for Classless Inter-Domain Routing. It replaced older fixed classes and allows precise subnet sizing using prefix lengths (for example, /24, /27, /30). That flexibility is now standard in modern networking, cloud infrastructure, firewall rules, and routing policies.
How CIDR notation works
IP + Prefix
CIDR notation has two parts:
- IPv4 address (e.g., 10.12.3.77)
- Prefix length (e.g., /22)
The prefix tells you how many bits belong to the network portion. The remaining bits are host bits. More network bits means smaller subnets; fewer network bits means larger subnets.
Common examples
- /24 → 256 total addresses, 254 usable (typical LAN segment)
- /27 → 32 total addresses, 30 usable
- /30 → 4 total addresses, often used for point-to-point links
- /32 → single host route
What this calculator returns
For each CIDR input, this page calculates:
- Subnet mask and wildcard mask
- Network address
- Broadcast address
- First and last usable host IP
- Total and usable address counts
- Prefix, host bits, binary subnet mask
- IP class and private/public scope hint
Practical subnetting walkthrough
Example: 192.168.50.139/26
A /26 means 64 addresses per subnet (26). Subnets increment by 64 in the final octet: 0, 64, 128, 192. Since 139 falls inside 128-191, the network is 192.168.50.128 and broadcast is 192.168.50.191. Usable host range becomes 192.168.50.129 - 192.168.50.190.
Why this matters in real systems
Correct CIDR calculations help avoid overlapping subnets, routing loops, and ACL mistakes. In cloud VPC design, this is especially important because poor planning can block future expansion. In enterprise networks, it impacts VLAN sizing, DHCP scopes, and security segmentation.
Tips for accurate subnet planning
- Leave growth room for future devices and services.
- Document network purpose per CIDR block (servers, clients, management, IoT, etc.).
- Keep critical network ranges contiguous when possible for cleaner route summarization.
- Validate every firewall and route entry with calculated network/broadcast boundaries.
- Use smaller subnets for sensitive segments to reduce lateral movement risk.
Quick CIDR reference table
- /16 → 65,536 total addresses
- /20 → 4,096 total addresses
- /24 → 256 total addresses
- /28 → 16 total addresses
- /29 → 8 total addresses
- /30 → 4 total addresses
Final thought
CIDR looks simple, but small mistakes create big operational issues. Use this calculator to quickly verify your addressing decisions before deploying infrastructure, updating route tables, or applying security policies. A few seconds of validation can save hours of troubleshooting.