CIDR Notation Calculator
Example Data Table
| Input CIDR | Network Address | Broadcast Address | Usable Hosts | Subnet Mask |
|---|---|---|---|---|
| 192.168.10.44/24 | 192.168.10.0 | 192.168.10.255 | 254 | 255.255.255.0 |
| 10.0.5.130/26 | 10.0.5.128 | 10.0.5.191 | 62 | 255.255.255.192 |
| 172.16.8.9/30 | 172.16.8.8 | 172.16.8.11 | 2 | 255.255.255.252 |
| 198.51.100.8/31 | 198.51.100.8 | 198.51.100.9 | 2* | 255.255.255.254 |
| 203.0.113.200/32 | 203.0.113.200 | 203.0.113.200 | 1 | 255.255.255.255 |
*The /31 example assumes RFC 3021 mode for point-to-point networking.
Formula Used
Subnet Mask = first n bits set to 1, remaining bits set to 0
Example: /24 = 11111111.11111111.11111111.00000000 = 255.255.255.0
Network Address = IP Address AND Subnet Mask
Wildcard Mask = 255.255.255.255 - Subnet Mask
Broadcast Address = Network Address OR Wildcard Mask
Total Addresses = 2^(32 - Prefix Length)
Usable Hosts = Total Addresses - 2
This is the traditional rule. The calculator also supports usable /31 addressing and exact-host /32 results.
How to Use This Calculator
- Enter a full CIDR block like 192.168.10.44/24, or enter an IPv4 address with a prefix length.
- You may provide a subnet mask instead of the prefix. The calculator will derive the prefix automatically.
- Enable RFC 3021 mode if you want /31 point-to-point networks to show two usable addresses.
- Enable the binary option when you need binary subnet training or audit-friendly output.
- Press Calculate CIDR to show the result above the form and below the header.
- Use the CSV button to export the current result table. Use the PDF button to save the visible result block.
FAQs
1) What is CIDR notation?
CIDR notation writes an IP address followed by a slash and prefix length. The prefix tells how many leading bits belong to the network portion, such as /24 or /27.
2) What is the difference between a subnet mask and a prefix?
They describe the same network boundary in different formats. A prefix uses bit count, like /24. A subnet mask uses dotted decimal, like 255.255.255.0.
3) Why does a /31 network sometimes show two usable addresses?
Point-to-point links can use both addresses in a /31 subnet under RFC 3021. This removes the traditional network and broadcast reservation for that special case.
4) What does a /32 mean?
A /32 represents one exact IPv4 address. It is commonly used for loopbacks, host routes, firewall rules, and device-specific routing entries.
5) How is the network address calculated?
The calculator performs a bitwise AND between the IPv4 address and the subnet mask. The result is the network address for that prefix.
6) What is a wildcard mask used for?
A wildcard mask is the inverse of the subnet mask. It is often used in access control lists, route filters, and matching rules where variable host bits matter.
7) Can I enter a subnet mask instead of a prefix length?
Yes. Enter a valid contiguous subnet mask, and the calculator will convert it into the matching prefix length automatically.
8) Why are usable hosts lower than total addresses?
Traditional IPv4 subnets reserve one address for the network and one for broadcast. That is why a normal subnet usually has two fewer usable addresses than total addresses.