What is the formula for the Subnet Calculator?
Subnet Calculator: size = 2^(32−prefix); network = floor(address/size) × size. Input definitions: address = IPv4 address; prefix = Prefix length. Use the selected convention throughout the calculation.
Technical utilities
Subnet Calculator
Determine the IPv4 network, mask, last address and address count from a prefix. For /31 the host count follows the point-to-point convention; /32 represents one address.
- Explicit formulas and worked examples
- Check your inputs, then calculate
- Data is calculated in this browser only
Check the stated input format, calculation convention and limits before using the result.
Check the example inputs, then calculate. Your values stay in this browser.
Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link.
Calculation notes
Understand the Subnet Calculator
Subnet Calculator validates ipv4 address, prefix length before applying the displayed equation. Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link.
How can I reproduce the Subnet Calculator example?
Subnet Calculator baseline input: IPv4 address: 192.168.1.10; Prefix length: 24. Output: Network = 192.168.1.0; Subnet mask = 255.255.255.0; Last address = 192.168.1.255; Address count = 256; Usable hosts (RFC 3021 for /31) = 254. Substitute these values into the displayed equation to reproduce the result.
How should I interpret the Subnet Calculator result?
- Read network with its stated unit and convention. The default example and the independent worked scenario use different inputs, so compare the assumptions before comparing the numbers.
- Change one input at a time and use the equation to explain the result; do not mix unit, grade-scale, time-zone or rounding conventions across comparisons.
What limits apply to the Subnet Calculator?
- Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link.
- VLSM planning, IPv6, network discovery and device configuration are not included.
Content and calculation reviewed:
Understand the calculation
How to use it and the math behind it
Four steps to check your inputs and results
- Determine the IPv4 network, mask, last address and address count from a prefix. For /31 the host count follows the point-to-point convention; /32 represents one address.
- Enter IPv4 address, Prefix length in the stated format. Baseline values are for reproduction.
- Check the output unit and convention: Read network with its stated unit and convention. The default example and the independent worked scenario use different inputs, so compare the assumptions before comparing the numbers.
- Change one input and compare the result. Only IPv4 is supported. /31 has no conventional broadcast address on a point-to-point link. VLSM planning, IPv6, network discovery and device configuration are not included.
Subnet Calculator: calculation relationships
The prefix fixes network bits and leaves 32−prefix host bits. A /30 has 2²=4 addresses; 192.0.2.6 belongs to the block 192.0.2.4–192.0.2.7 with mask 255.255.255.252. Under the traditional broadcast convention, two addresses are usable hosts. /31 point-to-point links and /32 addresses use the separately stated exceptions.
size = 2^(32−prefix); network = floor(address/size) × size
The detailed guide adds variable definitions, a reproducible example, a practice question and model limitations.
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