Subnet Calculator (IPv4 / CIDR)
Enter an IP address and a CIDR prefix (or subnet mask) to instantly get the network address, broadcast address, usable host range, host count, wildcard mask, IP class, and a binary breakdown. Free, no sign-up required.
How to use this subnet calculator
Type any IPv4 address (for example 192.168.1.10) and choose a CIDR prefix such as /24. The calculator does the binary math for you and shows every value you need to plan or troubleshoot a network — or to check your work while you study.
What the results mean
Network address — the first address in the block, with all host bits set to 0. It identifies the subnet itself and can't be assigned to a device.
Broadcast address — the last address, with all host bits set to 1. Traffic sent here reaches every host on the subnet; it also can't be assigned to a device.
Usable host range — every address between the network and broadcast addresses. These are the IPs you can actually assign to devices.
Subnet mask & wildcard — the mask marks which bits are network vs. host; the wildcard mask (its inverse) is what you use in Cisco ACLs and OSPF statements.
CIDR prefix — shorthand for the mask: /24 means the first 24 bits are the network portion.
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What is a subnet calculator?
A subnet calculator takes an IP address and a CIDR prefix (or subnet mask) and works out the network address, broadcast address, the range of usable host addresses, the host count, the wildcard mask, and the IP class — instantly, so you don't have to do the binary math by hand.
How do I calculate a subnet from a CIDR prefix?
The CIDR prefix (for example /24) is the number of network bits. The remaining bits are host bits. The network address is the IP with all host bits set to 0, the broadcast is the IP with all host bits set to 1, and the usable hosts are everything in between — 2 to the power of the host bits, minus 2 for the network and broadcast addresses.
How many usable hosts are in a /24 network?
A /24 has 8 host bits, giving 256 total addresses and 254 usable host addresses (256 minus the network and broadcast addresses).
What happens with a /31 or /32 subnet?
A /31 is used for point-to-point links (RFC 3021) and provides 2 usable addresses with no separate network or broadcast address. A /32 represents a single host address (a host route).