IP Subnet Calculator
Calculate network and broadcast addresses, usable host ranges, and subnet masks from CIDR notation.
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e.g. 192.168.1.10/24 or 10.0.0.5 255.255.0.0
Subnet results
How to use the IP Subnet calculator
Enter an IPv4 address with a CIDR prefix, like 192.168.1.10/24, or with a dotted subnet mask, like 10.0.0.5 255.255.0.0. Without a prefix the address is treated as a single host (/32).
You’ll get the network and broadcast addresses, subnet and wildcard masks, the usable host range and host counts. /31 and /32 are handled as point-to-point and single-host networks.
Formula
Mask = first N bits set to 1. Network = IP AND mask. Broadcast = Network OR (NOT mask). Total addresses = 2^(32 − N). Usable hosts = total − 2 for /0–/30, 2 for /31 (RFC 3021) and 1 for /32.
Frequently asked questions
What is CIDR notation?
Classless Inter-Domain Routing (CIDR) notation like /24 gives the number of leading 1-bits in the subnet mask, i.e. how many bits identify the network. /24 is the mask 255.255.255.0.
How many hosts can a /24 support?
A /24 has 256 addresses. The first is the network address and the last is the broadcast address, leaving 254 usable host addresses.
Why does a /31 have 2 usable hosts?
RFC 3021 allows /31 subnets on point-to-point links, where no network or broadcast address is needed, so both addresses are usable. A /32 identifies a single host and is common for loopbacks and host routes.
What is a wildcard mask?
The inverse of the subnet mask (0 bits become 1 and vice versa). It is used in Cisco ACLs and OSPF configuration — a /24 has the wildcard 0.0.0.255.