Subnet Mask Calculator

Enter any single parameter (Subnet Mask, CIDR, Host Count) to calculate all other values instantly.

Subnet Input Parameters

Base IP Address

CIDR Notation/24

Subnet Mask

Desired Usable Hosts

Network Interface Details

Network ID192.168.1.0

Broadcast Address192.168.1.255

Usable Host IP Range192.168.1.1 ~ 192.168.1.254

Wildcard Mask

0.0.0.255

Max Usable Hosts254 hosts

Binary Mask Structure Visualization

11111111.11111111.11111111.00000000

Network ID (Fixed Portion)

Host ID (Assignable Portion)

Networking Guide: The Art of Subnetting

What is a Subnet Mask? Binary 1s and 0sComputers process subnet masks as 32-bit binary values rather than decimal strings like 255.255.255.0. Contiguous 1s define the Network ID (unmodifiable prefix), while trailing 0s designate the Host ID (freely assignable addresses). A CIDR /24 simply means 24 leading binary 1s!

Why is Usable Hosts always 'Minus 2'?Two IP addresses in every subnet are reserved by protocol standards: the first address (all host bits set to 0) is the Network ID, naming the subnet segment. The final address (all host bits set to 1) is the Broadcast Address, used for sending packets to all subnet members. Neither can be assigned to endpoint devices, making the formula 2^n - 2.

Admin Pro Tip: What is a Wildcard Mask?A Wildcard Mask is the inverted binary mirror of a subnet mask—swapping binary 1s to 0s and 0s to 1s. It is required when configuring Cisco routers, OSPF routing, or firewall Access Control Lists (ACLs) (e.g., 0.0.0.255). Computing it manually is error-prone, so this tool generates it automatically!