🌐 IPv4 Subnet Calculator

IP Address

CIDR Prefix

What is the Subnet Calculator?

The Subnet Calculator takes an IPv4 address and a CIDR prefix (like /24) and works out every detail of that subnet: network address, broadcast address, subnet mask, wildcard mask, the first and last usable host addresses, the total number of usable hosts, and the IP address class.

How to Use It

Enter an IP address such as 192.168.1.100, choose a CIDR prefix from the dropdown — common options like /24, /28, or /30 are listed with their class labels — and click Calculate. The results panel fills in the full breakdown immediately, with addresses shown in standard dotted-decimal notation.

When to Use It

Use it when designing or troubleshooting a network: sizing a subnet for a given number of devices, splitting a larger block into smaller VLANs, verifying which addresses are usable versus reserved, or double-checking a subnet mask before configuring a router, firewall, or DHCP scope.

Who Benefits

Network administrators and IT technicians configuring routers and switches, students studying for networking certifications like CompTIA Network+ or Cisco CCNA, developers setting up cloud VPCs and security groups, and home-lab hobbyists planning their own network layout all get an instant, accurate subnet breakdown without manual binary math.

Frequently Asked Questions

CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its subnet mask together, like 192.168.1.0/24. The number after the slash is how many bits from the left are the network portion — /24 means the first 24 bits are network bits, equivalent to a 255.255.255.0 mask.

Every subnet reserves its first address as the network address and its last address as the broadcast address, so neither can be assigned to a device. A /24 subnet has 256 total addresses but only 254 usable host addresses. The exception is /31 and /32, which this calculator handles as point-to-point links or single hosts with no such reservation.

The wildcard mask is the inverse of the subnet mask — where the mask has a 1 bit, the wildcard has a 0, and vice versa. It's used in Cisco ACLs and OSPF configuration instead of a standard subnet mask, and this calculator computes it automatically alongside the regular mask.

🌐 Subnet Calculator