What is the difference between the network and broadcast address?

The network address is the first address in the block (all host bits set to 0) and identifies the subnet itself. The broadcast address is the last address (all host bits set to 1) and reaches every host on the subnet. Neither is normally assignable to a device, which is why a /24 with 256 total addresses gives 254 usable hosts.

How is the usable host count calculated?

For a prefix of length n the block holds 2^(32-n) total addresses. For prefixes /30 and shorter you subtract two (network + broadcast), so a /24 yields 256 - 2 = 254 usable hosts. A /31 has two usable addresses under RFC 3021 point-to-point links, and a /32 represents a single host.

What is a wildcard mask?

A wildcard mask is the bitwise inverse of the subnet mask: where the mask has a 1, the wildcard has a 0, and vice versa. For /24 the mask is 255.255.255.0 and the wildcard is 0.0.0.255. Wildcard masks are used in Cisco access control lists and OSPF network statements to describe which address bits must match.

Can I enter a subnet mask instead of a CIDR prefix?

Yes. The calculator accepts a CIDR prefix (10.0.0.0/16), a space-separated dotted mask (10.0.0.0 255.255.0.0) or a slash-separated dotted mask (10.0.0.0/255.255.0.0). It validates that the mask is a contiguous run of 1 bits and converts it to the equivalent prefix length.

What does the classful class tell me?

The class is the legacy classful interpretation derived from the first octet of the network address: Class A (0-127), B (128-191), C (192-223), D multicast (224-239) and E reserved (240-255). Modern routing is classless (CIDR), so the class is informational only — it does not change how the subnet is calculated.

Is my IP data kept private?

Completely. All subnet math runs in your browser using plain JavaScript bitwise operations. Nothing you type is ever sent to a server, logged or stored — there are no network requests at all.

Subnet Calculator — Gera Tools

A complete IPv4 subnet calculator that turns an address plus a prefix or mask into every value a network engineer needs: the network address, broadcast address, usable host range, host count, wildcard mask, the binary subnet mask, the classful class and the address scope. It is built for anyone planning an addressing scheme, writing router or firewall configuration, studying for a networking exam, or sanity-checking a VLAN before deploying it.

How it works

Enter an address in CIDR notation such as 192.168.1.10/24. Internally the tool parses the four octets into a single unsigned 32-bit integer, then builds the subnet mask by setting the leftmost n bits (where n is the prefix length). From there everything is pure bitwise arithmetic:

Network = address AND mask (clears all host bits to 0).
Broadcast = network OR wildcard (sets all host bits to 1).
Wildcard = NOT mask (the inverse of the subnet mask).
Usable range = network + 1 through broadcast − 1 for prefixes /30 and shorter.

Two special cases are handled correctly: a /31 is treated as an RFC 3021 point-to-point link with two usable addresses and no broadcast reservation, and a /32 represents a single host. You can also paste a dotted-decimal mask such as 255.255.255.0 in place of the prefix — the calculator verifies the mask is a valid contiguous run of 1 bits and converts it to the matching prefix length. The results table additionally reports the legacy classful class from the first octet and the scope (private RFC 1918, loopback, link-local APIPA, CGN, multicast, reserved or public), so you can immediately tell whether a block is routable on the public internet.

Example

Take 192.168.1.10/24. The mask is 255.255.255.0, so:

Network address: 192.168.1.0
Broadcast address: 192.168.1.255
Usable host range: 192.168.1.1 – 192.168.1.254
Total addresses: 256, usable hosts: 254
Wildcard mask: 0.0.0.255, scope: Private (RFC 1918)

Change the prefix to /26 and the same address resolves to network 192.168.1.0, broadcast 192.168.1.63, and 62 usable hosts — exactly what you would assign to a small VLAN.

CIDR	Mask	Total	Usable hosts
/24	255.255.255.0	256	254
/26	255.255.255.192	64	62
/30	255.255.255.252	4	2
/31	255.255.255.254	2	2

Every figure is computed locally in your browser — no addresses are uploaded or stored.