CIDR CALCULATOR

CIDR / Subnet Calculator

Enter an IPv4 network in CIDR notation to see its mask, range and host count.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) writes an IP network as an address plus a prefix length, like 192.168.1.0/24. The prefix is how many leading bits are fixed as the network part — /24 means the first 24 bits identify the network and the remaining 8 bits are for hosts, giving 256 addresses. From the CIDR this calculator derives the network and broadcast addresses, the subnet mask and its wildcard, the usable host range and how many hosts the block holds.

FAQ

How many hosts are in a /24, /16 or /8?

A /24 has 256 addresses (254 usable), a /16 has 65,536 (65,534 usable), and a /8 has 16,777,216. The usable count is total minus 2 — one address is the network, one is the broadcast — except /31 and /32, which are used whole for point-to-point links and single hosts.

What is the difference between netmask and wildcard?

The netmask marks the network bits as 1s (255.255.255.0 for /24). The wildcard is its inverse (0.0.0.255) — the host bits as 1s. Routers and firewalls (notably Cisco ACLs) often want the wildcard instead of the netmask, so the calculator shows both.

What are the network and broadcast addresses?

The network address is the first address in the block (all host bits 0) and names the subnet itself; the broadcast address is the last (all host bits 1) and reaches every host at once. Neither is assigned to a device, which is why they’re excluded from the usable range.

What do private ranges like 10.0.0.0/8 mean?

They’re address blocks reserved for internal networks (RFC 1918): 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. They aren’t routable on the public internet, so many networks reuse them behind NAT — which is why your home devices often sit in 192.168.x.x.

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