What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation is a compact way to specify an IP address and its associated network mask. For example, 192.168.1.0/24 means the first 24 bits are the network portion.

What is the difference between subnet mask and wildcard mask?

A subnet mask marks network bits as 1s and host bits as 0s (e.g. 255.255.255.0). A wildcard mask is the inverse — host bits are 1s and network bits are 0s (e.g. 0.0.0.255). Wildcard masks are used in ACLs and OSPF.

Why are there fewer usable hosts than total addresses?

In any subnet, two addresses are reserved: the network address (all host bits 0) and the broadcast address (all host bits 1). So usable hosts = total addresses - 2, except for /31 and /32 subnets.

Is this calculation done in my browser?

Yes. All subnet calculations are performed locally using pure math on 32-bit integers. No data is sent to any server.

IP Subnet Calculator

Calculate subnet details from an IP address and CIDR prefix length.

IP Address

CIDR (/24)

Subnet Details

Network Address192.168.1.0

Broadcast Address192.168.1.255

First Usable Host192.168.1.1

Last Usable Host192.168.1.254

Total Hosts256

Usable Hosts254

Subnet Mask255.255.255.0

Wildcard Mask0.0.0.255

How to Use IP Subnet Calculator

Step 1

Enter an IPv4 address (e.g. 192.168.1.100).

Step 2

Select a CIDR prefix length (0-32) using the dropdown.

Step 3

View the calculated subnet details instantly.

Step 4

Use the results for network configuration or planning.

Features

Calculates network address, broadcast address, and usable host range.

Shows total host count and usable host count.

Displays subnet mask and wildcard mask.

Supports all CIDR prefix lengths from /0 to /32.

Real-time calculation as you type.

Completely client-side — no data sent to any server.

FAQ

: CIDR (Classless Inter-Domain Routing) notation is a compact way to specify an IP address and its associated network mask. For example, 192.168.1.0/24 means the first 24 bits are the network portion.
: A subnet mask marks network bits as 1s and host bits as 0s (e.g. 255.255.255.0). A wildcard mask is the inverse — host bits are 1s and network bits are 0s (e.g. 0.0.0.255). Wildcard masks are used in ACLs and OSPF.
: In any subnet, two addresses are reserved: the network address (all host bits 0) and the broadcast address (all host bits 1). So usable hosts = total addresses - 2, except for /31 and /32 subnets.
: Yes. All subnet calculations are performed locally using pure math on 32-bit integers. No data is sent to any server.