What this online CIDR calculator does
This online CIDR calculator helps you quickly convert an IP address and subnet prefix into practical network details. Instead of manually doing binary math, you can immediately see the network address, broadcast address, host range, subnet mask, wildcard mask, and total/usable addresses.
CIDR stands for Classless Inter-Domain Routing. It replaces older class-based subnet sizing and gives you flexible control over how large or small a subnet should be. If you work in IT, cloud, DevOps, security, or home networking, CIDR notation is everywhere.
How to use the calculator
Step-by-step
- Enter an IPv4 address (example:
192.168.1.34). - Enter a prefix length from
0to32(example:24). - Click Calculate CIDR.
- Review the generated network and host details.
You can also enter a combined value such as 10.0.0.18/16 directly in the IP field. The calculator
will parse the prefix automatically.
Understanding the results
- Network Address: The first address in the subnet (subnet identifier).
- Broadcast Address: The last address in the subnet (used to reach all hosts in classic IPv4 broadcast domains).
- First/Last Usable Host: Normal host range for device assignment.
- Subnet Mask: Dotted decimal equivalent of the prefix (example
/24 = 255.255.255.0). - Wildcard Mask: Inverse of subnet mask; useful in ACL and routing contexts.
- Total Addresses: All addresses in subnet, including network and broadcast (except special cases).
- Usable Hosts: Host addresses generally assignable to interfaces.
Common CIDR prefixes and subnet sizes
| CIDR | Subnet Mask | Total Addresses | Typical Usable Hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /24 | 255.255.255.0 | 256 | 254 |
| /27 | 255.255.255.224 | 32 | 30 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 (point-to-point links) |
| /32 | 255.255.255.255 | 1 | 1 (single host route) |
Why CIDR matters in modern networks
CIDR allows route aggregation and efficient address allocation. That means smaller routing tables, cleaner designs, and less waste of IPv4 space. In cloud platforms (AWS, Azure, GCP), VPC and subnet planning relies heavily on CIDR blocks. Security groups, NACLs, VPN routes, and peering rules all require precise subnet calculations.
Common mistakes to avoid
- Mixing up network and broadcast with usable host addresses.
- Choosing overlapping CIDR ranges when designing multiple subnets.
- Using an overly small subnet that cannot scale with future hosts.
- Forgetting special handling of
/31and/32in routing and point-to-point links.
Quick FAQ
Is this calculator for IPv4 or IPv6?
This tool is built for IPv4 CIDR calculations.
Can I subnet private and public IP ranges?
Yes. The calculator works for both. It also labels whether an address is private, public, loopback, link-local, etc.
Do I need to understand binary to use this?
No, but understanding binary subnetting helps. The tool includes binary mask/network output so you can learn while you calculate.