CIDR Calculator

Formula

Prefix bits set to 1

Worked example

/24 — 255.255.255.0

Quick answer

What does the CIDR Calculator do?

Calculate IPv4 subnet mask from CIDR prefix.

What is the CIDR Calculator?

Calculate IPv4 subnet mask from CIDR prefix. Use it when you have the required inputs and want a deterministic, repeatable result with the calculation method visible.

How to use this calculator

Enter the values requested by the tool, keep units and time periods consistent, resolve any validation message, calculate, then review the primary answer together with the displayed formula and supporting values.

Formula and method

This calculator uses the deterministic formula Prefix bits set to 1. Enter the required values, then review the displayed substitution and result breakdown to verify the calculation.

Worked example

/24 255.255.255.0

Common mistakes to avoid

Check units, decimal points, percentages, signs, date/time order, selector choices, and rounding. For important decisions, verify the result against an independent source or qualified professional when appropriate.