What is a subnet mask?

A subnet mask is a 32-bit number that divides an IP address into a network portion and a host portion. It is written in dotted-decimal form (e.g. 255.255.255.0) and always consists of consecutive 1-bits followed by consecutive 0-bits.

What does the CIDR prefix length mean?

The prefix length (e.g. /24) is the number of leading 1-bits in the subnet mask. /24 corresponds to 255.255.255.0, meaning the first 24 bits identify the network and the remaining 8 bits identify hosts.

How many usable hosts does a /24 subnet have?

A /24 subnet has 256 total addresses (2^8). Two are reserved — the network address and the broadcast address — leaving 254 usable host addresses.

What is the difference between network address and broadcast address?

The network address is the first address in a subnet (all host bits set to 0) and identifies the subnet itself. The broadcast address is the last address (all host bits set to 1) and is used to send packets to all hosts in the subnet simultaneously.

Can I enter the IP and prefix together?

Yes. You can type the address in CIDR notation directly in the IP field (e.g. 10.0.0.1/16) and the tool will split the prefix length automatically.

Does this tool support IPv6?

No. This tool is designed for IPv4 addresses only (32-bit). IPv6 subnetting follows different rules and requires a separate calculator.

Subnet Mask Calculator

Name: Subnet Mask Calculator
Availability: InStock
Author: Nham Vu

Enter an IPv4 address and CIDR prefix (e.g. 192.168.1.50/24) to instantly see the subnet mask, network address, broadcast address, host range, and usable host count.

IPv4 Subnet Input

IP Address

You may include the prefix here (e.g. 10.0.0.1/8).

CIDR Prefix Length

Enter a value from 0 to 32.

Quick Prefix Examples

Enter an IP address and prefix length, then click Calculate.

Subnet Results

IP Address

Prefix Length

Subnet Mask

Mask (binary)

Wildcard Mask

Network Address

Broadcast Address

First Usable Host

Last Usable Host

Usable Hosts

Total Addresses

IP Class

Binary Breakdown

Label	Binary (32 bits)

Network bits Host bits

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Summary

Enter an IPv4 address and CIDR prefix (e.g. 192.168.1.50/24) to instantly see the subnet mask, network address, broadcast address, host range, and usable host count.

How it works

Enter an IPv4 address in dotted-decimal notation (e.g. 192.168.1.100).
Enter a CIDR prefix length between 0 and 32, or type the full address with slash notation (e.g. 192.168.1.100/24).
Click "Calculate" — the tool derives the 32-bit subnet mask from the prefix length.
It ANDs the IP with the subnet mask to find the network address.
The broadcast address is found by ORing the network address with the inverted mask.
Usable hosts are all addresses between network + 1 and broadcast - 1.

Use cases

Plan IP address allocation for office or home networks.
Verify subnetting homework and CCNA exam practice.
Troubleshoot routing issues by confirming network boundaries.
Design VPC or cloud network CIDR blocks.
Split a large network into smaller subnets for security zones.
Check whether two IP addresses belong to the same subnet.
Quickly find the broadcast address for directed broadcasts.
Document network topology with accurate subnet parameters.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu