CIDR Calculatorv1.0.0

Enter an IP address with or without CIDR notation to compute the full subnet breakdown. The calculator accepts standard dotted-decimal format with an optional prefix length (for example, 192.168.1.0/24). If no prefix is provided, select one from the Prefix Length dropdown, which lists every value from /0 to /32.

• Type an IP address into the IP Address / CIDR Notation field. Include the prefix length after a forward slash (10.0.0.0/8) or leave it off and pick a prefix from the dropdown.
• When a prefix is included in the text field, the Prefix Length dropdown updates automatically to match. Changing the dropdown also updates the text field.
• Press Calculate or wait briefly for automatic calculation. Results appear below the input area and include the network address, broadcast address, subnet mask, wildcard mask, first and last usable hosts, total addresses, and usable host count.
• Open Settings to enable binary representations, which display each address as a 32-bit binary string grouped into octets. A second option in settings reveals step-by-step calculation details showing the bitwise AND operation that derives the network address from the input IP and subnet mask.
• Special prefix lengths receive accurate treatment. A /32 prefix describes a single host with no broadcast, a /31 prefix defines a point-to-point link with two usable addresses, and a /0 prefix covers the entire IPv4 space.
• Press Reset to clear all saved state and restore the default input of 192.168.1.0/24.
• All inputs and settings persist in local storage, so returning to the page restores the previous session.

Subnet calculations appear in network planning, security auditing, cloud infrastructure provisioning, and education. The following scenarios illustrate where a CIDR calculator fits into common workflows.

• Network Design: Plan a corporate LAN by entering the allocated address block (172.16.0.0/20) and reading off the 4094 usable host addresses, the broadcast boundary, and the wildcard mask needed for access control lists.
• Cloud Infrastructure: Size a VPC subnet on AWS, Azure, or GCP by testing different prefix lengths against the required instance count. A /24 provides 254 usable addresses while a /21 yields 2046.
• Firewall Rules: Verify that a proposed CIDR block covers the intended range and does not inadvertently include addresses outside the target scope. Compare the first and last usable host against the intended boundaries.
• Education: Study subnetting by toggling on binary representations and step-by-step calculations. Observe how the bitwise AND between the IP address and the subnet mask produces the network address, and trace the relationship between prefix length and available hosts.
• Troubleshooting: Determine whether two devices reside on the same subnet by entering each address with the configured prefix length and comparing the resulting network addresses.
• Documentation: Generate precise subnet details for network documentation, including the full host range, broadcast address, and wildcard mask, without manual binary math. Enable binary representations to include the 32-bit notation alongside each address for low-level reference material.
• Security Auditing: Validate that publicly exposed CIDR ranges match the intended allocation by checking the total address count and boundary addresses against the security policy.