CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses. It replaces the old classful system with flexible prefix lengths, written as IP/prefix (e.g., 10.0.0.0/8).

How is this different from the Subnet Calculator?

The Subnet Calculator takes an IP and prefix as separate inputs. The CIDR Calculator takes a single CIDR notation string (IP/prefix) and parses it automatically.

What prefixes are valid?

Valid CIDR prefixes range from /0 (entire IPv4 space) to /32 (single host). Common values are /8, /16, /24, and /28.

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CIDR Calculator

Calculate network details from CIDR notation instantly.

CIDR Notation

About this tool

Free online CIDR calculator. Enter a CIDR block (e.g., 10.0.0.0/16) to compute network address, broadcast address, subnet mask, wildcard mask, and host counts. Runs entirely in your browser.

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