IP Subnet / CIDR Calculator

IP Subnet / CIDR is evaluated from CIDR Prefix Length. The calculation reports Subnet Mask, Total Addresses and Usable Host Addresses.

Results

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About the IP Subnet / CIDR Calculator

IP Subnet / CIDR is treated here as a quantitative relation between CIDR Prefix Length and Subnet Mask, Total Addresses, Usable Host Addresses and Wildcard Mask.

The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.

Formula basis:
Total IPs = 2^(32 - prefix_length)
Usable hosts = Total - 2
Subnet mask: first prefix bits = 1, remainder = 0

Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.

Formula & How It Works

The calculation applies the following relations exactly as recorded in the metadata:

Total IPs = 2^(32 - prefix_length)
Usable hosts = Total - 2
Subnet mask: first prefix bits = 1, remainder = 0

Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.

Worked Examples

Example 1: /24 network — typical home/small office subnet

Inputs

cidr: 24
Subnet Mask: 255.255.255.0. Total Addresses: 256. Usable Host Addresses: 254. Wildcard Mask: 0.0.0.255

With CIDR Prefix Length = 24 as the stated inputs, the result is Subnet Mask = 255.255.255.0, Total Addresses = 256 and Usable Host Addresses = 254. Each value corresponds to the declared output fields.

Example 2: /16 network — medium enterprise

Inputs

cidr: 16
Subnet Mask: 255.255.0.0. Total Addresses: 65,536. Usable Host Addresses: 65,534. Wildcard Mask: 0.0.255.255

With CIDR Prefix Length = 16 as the stated inputs, the result is Subnet Mask = 255.255.0.0, Total Addresses = 65,536 and Usable Host Addresses = 65,534. Each value corresponds to the declared output fields.

Example 3: /30 network — point-to-point link between routers

Inputs

cidr: 30
Subnet Mask: 255.255.255.252. Total Addresses: 4. Usable Host Addresses: 2. Wildcard Mask: 0.0.0.3

With CIDR Prefix Length = 30 as the stated inputs, the result is Subnet Mask = 255.255.255.252, Total Addresses = 4 and Usable Host Addresses = 2. Each value corresponds to the declared output fields.

Example 4: /28 — small DMZ or IoT segment

Inputs

cidr: 28
Subnet Mask: 255.255.255.240. Total Addresses: 16. Usable Host Addresses: 14. Wildcard Mask: 0.0.0.15

With CIDR Prefix Length = 28 as the stated inputs, the result is Subnet Mask = 255.255.255.240, Total Addresses = 16 and Usable Host Addresses = 14. Each value corresponds to the declared output fields.

Common Use Cases

  • Calculate usable hosts in a subnet
  • Find network and broadcast addresses
  • Plan IP address allocation for a network