Enter an IPv4 CIDR block to see its network details.
A subnet calculator turns an IP address and a prefix length into the numbers you actually need: which addresses belong to the network, which one is the broadcast address, how many hosts fit, and what the netmask and wildcard mask look like.
Enter an address in CIDR form — for example 192.168.1.0/24 — to see the full breakdown.
The number after the slash is the prefix length: how many bits, counting from the left, are fixed as the network portion of the address. Everything after those bits identifies a host inside that network.
So in 192.168.1.0/24, the first 24 bits (192.168.1) name the network and the remaining 8 bits are free for hosts — 256 addresses in total. Make the prefix shorter and the network gets bigger: a /23 covers 512 addresses, a /16 covers 65,536. Each step down doubles the size.
In a normal IPv4 subnet, two addresses are reserved. The first is the network address, which names the subnet itself, and the last is the broadcast address, which reaches every host at once. Neither can be assigned to a machine, so a /24 with 256 addresses gives you 254 usable ones.
There are two edge cases worth knowing. A /31 has no room for either reserved address and is defined specifically for point-to-point links, where both addresses are usable. A /32 describes exactly one address and is how you refer to a single host in a routing table or firewall rule.
The netmask is the same information as the prefix length, written as four octets — a /24 is 255.255.255.0. Older equipment and most operating system network settings still expect this form.
The wildcard mask is the netmask inverted, and it turns up mainly in access control lists on network hardware. Where a netmask uses 1 bits to mean "this part must match", a wildcard uses 0 bits for the same thing, which is a common source of off-by-one confusion when copying rules between systems.
Three IPv4 ranges are reserved for private use and are never routed on the public internet. If your device reports one of these, you are behind a router doing network address translation:
10.0.0.0/8 — 10.0.0.0 to 10.255.255.255, common in larger corporate networks172.16.0.0/12 — 172.16.0.0 to 172.31.255.255, often used by container and VPN software192.168.0.0/16 — 192.168.0.0 to 192.168.255.255, the default for nearly every home routerIt means the first 24 bits of the address identify the network and the remaining 8 bits identify hosts within it. That gives 256 total addresses, of which 254 are usable, and corresponds to the netmask 255.255.255.0.
Take 2 to the power of the number of host bits, then subtract 2 for the network and broadcast addresses. A /24 has 8 host bits, so 2^8 = 256 total and 254 usable. A /30 has 2 host bits, so 4 total and 2 usable.
They carry the same information inverted. A netmask marks the network portion with 1 bits, so /24 is 255.255.255.0. The matching wildcard mask is 0.0.0.255. Netmasks are used in interface configuration, wildcard masks mostly in router access control lists.
The first address identifies the network itself and the last is the broadcast address for reaching every host on it. Both have special meaning in IP routing, so neither can be assigned to a device. The exception is a /31 point-to-point link, where both addresses are usable.
An address in one of the ranges reserved for internal networks — 10.0.0.0/8, 172.16.0.0/12 or 192.168.0.0/16. These are not routed on the public internet, so many networks can reuse the same private addresses behind their own routers.