NETWORK UTILITY

IP Range Calculator

Find the boundaries of an IPv4 CIDR block without sending the address anywhere.

IP Range CalculatorIPv4

Find the start and end of an IPv4 CIDR range

The calculator identifies the network boundary and last address in the block, then shows traditional usable-host boundaries. It is useful when reviewing firewall rules, network documentation and allocations.

This tool calculates mathematical address boundaries. It does not test whether an address is active, reachable or assigned to a particular device.

Example

203.0.113.17/28 represents a 16-address block. The CIDR prefix defines the boundaries; the host value you type can be anywhere inside that block.

Why IP range boundaries matter

Network rules are frequently written as CIDR blocks rather than individual addresses. Knowing the exact first and last address helps when reviewing allowlists, firewall scopes, routing policies and provider allocations.

The address you enter can be anywhere inside the block

If you enter an address such as 203.0.113.17/28, the calculator first applies the prefix to determine the actual network boundary. The input address does not need to be the network address itself.

Range size grows quickly

Each time the prefix becomes one bit shorter, the number of addresses doubles. A /24 has 256 addresses, a /23 has 512, and a /22 has 1,024. That is why small prefix changes can have large operational consequences.