The CIDR calculator takes an IPv4 address in CIDR notation (like 192.168.1.0/24) and instantly computes the network address, broadcast address, subnet mask, wildcard mask, usable IP range, and host count. It's a standard tool for network planning, subnet design, and firewall ACL configuration.
What each output field means
For 192.168.1.0/24, the tool outputs:
- Network address —
192.168.1.0, the subnet identifier (host bits all zero) - Broadcast address —
192.168.1.255, the last address (host bits all one) - Subnet mask —
255.255.255.0, binary11111111.11111111.11111111.00000000 - Wildcard mask —
0.0.0.255, the inverse of the subnet mask; used in Cisco ACL and OSPF config - Usable range —
192.168.1.1 – 192.168.1.254, 254 addresses - Host count — total = 2^(32 − prefix); usable = total − 2 (excludes network and broadcast)
Prefix length and capacity reference
Small networks
- /30 — 2 usable hosts, router point-to-point links
- /29 — 6 usable hosts, small server clusters
- /28 — 14 usable hosts
- /27 — 30 usable hosts
- /24 — 254 usable hosts, home and office standard
Larger networks
- /23 — 510 usable hosts
- /22 — 1,022 usable hosts
- /20 — 4,094 usable hosts
- /16 — 65,534 usable hosts, enterprise LAN or VPC
- /8 — ~16.7 million usable hosts, ISP scale
/31 and /32 special cases
/31 is a point-to-point subnet defined in RFC 3021. Both addresses are assignable — there is no separate network address or broadcast address. The tool does not subtract 2 from the host count for /31.
/32 identifies a single host (e.g., 8.8.8.8/32) and is used in routing policy to target a specific device or configure a host route.
Checking whether two IPs are in the same subnet
Enter each IP separately and compare the network address field. If they match, the IPs are in the same subnet. For example, 192.168.1.50/25 has network address 192.168.1.0 and 192.168.1.200/25 has 192.168.1.128 — different subnets, even though they share the same /24 block.
VPC subnet planning tips
When carving subnets inside a private range (10.0.0.0/8 or 172.16.0.0/12), a common pattern is to allocate /20 blocks (4,094 hosts) per application tier and reserve /24 to /27 slices for specific services like databases and NAT gateways. Use the calculator to verify address ranges don't overlap before committing, since CIDR conflicts are painful to fix after deployment.