IPv4 Subnet Calculator

Enter four decimal address components from zero through 255, separated by dots. Leading zeros are rejected to avoid ambiguous notation. The address can be any address inside the network you are describing; it does not have to be the network’s first address.

Enter a whole-number prefix from zero through 32. The prefix counts network bits. A larger prefix leaves fewer host bits and creates a smaller containing block. The subnet calculator shows the corresponding dotted-decimal mask so you can compare the two representations directly.

Read the network, last address, conventional usable range and count together. For prefixes through /30, the conventional subnet calculation excludes the network and directed-broadcast addresses from the host count. These are arithmetic conventions, not a discovery of which machines are online.

Check the /31 and /32 labels before copying. A /31 is treated as a point-to-point pair with two endpoint addresses and no directed broadcast. A /32 represents one host. Do not apply the familiar subtract-two formula blindly to these cases or use their special rules for a different deployment model.

An IPv4 address has 32 bits. If the network prefix is p, the containing block has 2 to the power of 32 minus p addresses. The subnet calculator locates the block containing the input address and derives the mask and boundaries from that size. For example, 192.168.1.42 with /24 belongs to 192.168.1.0/24. The conventional broadcast address is 192.168.1.255, with 254 conventional host addresses between the endpoints. This calculation does not know which addresses your DHCP server reserves or whether your equipment uses the same network configuration.

A subnet calculator cannot identify free addresses. An address inside the usable range may already be assigned, reserved or intentionally unused. Consult the network configuration you administer before assigning an address.

The /0 result is an arithmetic address-space range, not a suggestion that every address in it is publicly routable or available for allocation. Special-use ranges and routing policy are separate matters.

This component calculates IPv4 only. IPv6 subnet planning uses different address notation and operational conventions. It would be misleading to accept an IPv6 string and silently reinterpret it as an IPv4 result.

For 192.168.1.42/24, the host portion has eight bits, giving 256 total addresses. Conventional subnet rules reserve the network and broadcast endpoints, leaving 254 host addresses. Changing the prefix to /25 leaves seven host bits and a block of 128 addresses. The same input address then belongs to the lower half of the former /24, with different boundaries. This shows why the prefix cannot be omitted: the address alone does not uniquely determine a subnet. Save the address and prefix together, and distinguish calculated capacity from actual address availability.

Keep the question, input, observation time and source together. A bare address, percentage or status code is difficult to interpret later because it omits the connection and measurement context. When comparing two observations, note what changed between them: the target, network, VPN state, selected adapter, record type or remote origin. Change one relevant condition at a time when possible. That makes the comparison easier to explain without inventing a cause from one number.

Save only information you actually need. Network records can reveal infrastructure names and connection details, even when they do not contain a password. Remove unrelated identifiers before sharing a screenshot with another person. Never put private credentials in a domain field or publish an internal hostname as part of a public test. A copied result is a snapshot, not a promise that the same conditions still apply when someone reads it later.

Kepo is a Mac desktop-widget product for repeated checks and small workflows. A labeled troubleshooting note or a supported monitoring widget can keep the relevant context accessible while you work. The download link opens the product workflow; this article does not automatically install a configured diagnostic widget, transfer your network inputs or start a scheduled check. Confirm the actual widget’s capabilities before relying on it for ongoing observations.