IPv4 Subnet Calculator

Enter an IPv4 address and CIDR prefix to instantly get the network address, broadcast address, netmask, wildcard mask, usable host range and host counts. Everything runs locally in your browser.

How to use this subnet calculator

Enter an IPv4 address together with its CIDR prefix length, either combined as 192.168.1.10/24 or with the prefix typed separately after a slash. Click Calculate to see the full breakdown: the network and broadcast addresses that bound the subnet, the netmask and its inverse (wildcard mask), the first and last usable host addresses, and the total versus usable host counts. Invalid input — an octet outside 0–255 or a prefix outside 0–32 — shows a clear error instead of producing garbage output.

Understanding CIDR and subnetting

CIDR (Classless Inter-Domain Routing) notation expresses a subnet as an IP address plus a prefix length, such as /24, indicating how many leading bits of the address are fixed as the network portion. A /24 network has 8 bits left for hosts, giving 256 total addresses — 254 usable once you subtract the network and broadcast addresses. Point-to-point links commonly use /30 (2 usable hosts) or /31 (2 usable hosts with no network/broadcast reserved, per RFC 3021). Subnetting is fundamental to network design: it lets you split a large address block into smaller, routable segments that match the size of each LAN, VLAN, or link, minimizing wasted addresses and containing broadcast traffic.