Use this free subnet calculator to break down any IPv4 address and subnet mask. Enter your IP and either a dotted-decimal mask (e.g. 255.255.255.0) or a CIDR prefix (e.g. /24) — the two fields stay in sync automatically. The calculator instantly shows your network address, broadcast, usable host range, wildcard mask, and a colour-coded binary breakdown.
Subnet & CIDR Calculator
Enter an IP address along with either a subnet mask or CIDR prefix. The two fields stay in sync automatically — change one and the other updates instantly.
Results
Common Subnets — Quick Reference
| CIDR | Subnet Mask | Usable Hosts | Typical Use |
|---|
How to read the results
Network address — the first address in the subnet, used to identify the network itself. It cannot be assigned to a host.
Broadcast address — the last address in the subnet. Packets sent to this address are delivered to every host on the network. It also cannot be assigned to a host.
Usable hosts — the number of addresses you can actually assign to devices. For a /24, that is 254 (256 minus the network and broadcast addresses).
Wildcard mask — the inverse of the subnet mask. Used in access control lists (ACLs) on routers and firewalls to define which bits of an address to match.
The binary display colour-codes each bit: blue bits are the network portion (fixed) and red bits are the host portion (variable).
What is subnetting?
Subnetting is the process of dividing a larger IP network into smaller, more manageable segments called subnets. It gives network administrators control over which devices can communicate directly with each other and which traffic must pass through a router.
The subnet mask determines where the network portion of an IP address ends and the host portion begins. A /24 mask (255.255.255.0) means the first 24 bits identify the network and the remaining 8 bits identify individual hosts — giving you 254 usable addresses.
CIDR (Classless Inter-Domain Routing) notation is shorthand for the same information. /24 means 24 network bits; /16 means 16 network bits (a class B network with 65,534 usable hosts).
For more on networking fundamentals, see our guide to networking hardware and setup.
