Calculator Inputs
Enter CIDR notation directly, or provide the IP address and prefix separately. Subnet mask input is optional and auto-fills the prefix.
Example Data Table
| Input CIDR | Network Address | Usable Range | Broadcast | Usable Hosts |
|---|---|---|---|---|
| 192.168.1.34/24 | 192.168.1.0 | 192.168.1.1 - 192.168.1.254 | 192.168.1.255 | 254 |
| 10.10.5.130/26 | 10.10.5.128 | 10.10.5.129 - 10.10.5.190 | 10.10.5.191 | 62 |
| 172.16.40.9/20 | 172.16.32.0 | 172.16.32.1 - 172.16.47.254 | 172.16.47.255 | 4094 |
Formula Used
1) Total addresses: 2(32 - prefix)
2) Usable hosts: For prefixes below /31, usable hosts = total addresses - 2. For /31, both addresses are usable in point-to-point links. For /32, exactly one address exists.
3) Network address: Convert the IP and mask to 32-bit integers, then apply a bitwise AND operation.
4) Broadcast address: Broadcast = network address + total addresses - 1.
5) Wildcard mask: Wildcard = 255.255.255.255 - subnet mask.
6) Reserved planning: Available planned hosts = floor(usable hosts × (1 - reserve % / 100)).
How to Use This Calculator
- Enter a full CIDR block like 192.168.10.25/27, or fill the IP and prefix fields.
- Optionally enter a subnet mask. The calculator converts it to a prefix automatically.
- Add planned subnets and a reserved host percentage for capacity planning.
- Press Calculate CIDR Block to show the result above the form.
- Review network range, wildcard mask, binary mask, class, and usable host totals.
- Use the CSV or PDF buttons to export the result table.
Frequently Asked Questions
1. What does CIDR mean?
CIDR stands for Classless Inter-Domain Routing. It expresses an IP block using an address and prefix length, such as 10.0.0.0/24.
2. Why is the network address different from my entered IP?
Your entered IP may be a host inside the subnet. The network address is the first address in that block after the subnet mask is applied.
3. What is the broadcast address?
The broadcast address is the last address in a subnet. Traditional IPv4 networks use it to send traffic to all hosts within that block.
4. How are usable hosts calculated?
For most subnets, usable hosts equal total addresses minus two. The exceptions are /31 for point-to-point links and /32 for single-host routes.
5. What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. It is often used in routing, firewall, and access control list configurations.
6. Can I use this for VPC or cloud subnet planning?
Yes. It helps estimate address ranges, capacity, and subnet sizes for cloud networks, labs, VLANs, and segmented security zones.
7. Does this calculator support IPv6?
No. This version is focused on IPv4 CIDR calculations. IPv6 uses a different address format and typically much larger prefix spaces.
8. Why add a reserved host percentage?
Reserved capacity helps you avoid exhausting the subnet immediately. It is useful for growth planning, failover addresses, and infrastructure overhead.