Subnet Calculator

Use this subnet calculator to split an IPv4 network into smaller subnets.

You can divide a network by:

Number of subnets
Hosts per subnet

The tool then returns the resulting subnet ranges with:

Network address
First usable IP
Last usable IP
Broadcast address
Usable host count

What This Subnet Calculator Does

This is a classic IPv4 subnetting tool for equal-size subnet splitting.

It helps with common networking tasks such as:

Breaking a larger network into smaller subnets
Planning lab environments
Checking subnet masks and broadcast ranges
Studying subnetting for certification work
Validating how many hosts fit inside a subnet

If you enter:

10.0.0.0/16
split by 8 subnets

the calculator returns the resulting /19 networks.

If you enter:

10.0.0.0/16
split by 200 hosts per subnet

the calculator finds the smallest subnet size that supports that host requirement and lists the resulting subnets.

Split by Number of Subnets

Use this mode when you know how many subnets you need.

Example:

Base network: 10.0.0.0/16
Required subnets: 8

Result:

8 equal-size /19 subnets

This is useful for:

Dividing a larger allocation across sites or teams
Creating equal-size VLAN or lab segments
Checking how many subnet bits are required

CCNA-style explanation

If you start with 10.0.0.0/16 and need 8 subnets:

8 subnets requires 3 subnet bits because 2^3 = 8
Add those 3 bits to the original /16
New prefix = /19

That gives you:

8 equal-size subnets
8192 total IPs per subnet
8190 usable hosts per subnet

This is the exact type of subnetting logic used in CCNA and other network certification questions.

Split by Hosts per Subnet

Use this mode when you know how many hosts each subnet must support.

Example:

Base network: 10.0.0.0/16
Hosts per subnet: 200

Result:

The smallest matching equal-size subnet
All resulting subnet ranges inside the base network

This is useful when planning:

Office subnets
Training labs
Device segments
Server or VM ranges

CCNA-style explanation

If you start with 10.0.0.0/16 and need 200 hosts per subnet:

A /25 gives 126 usable hosts, which is too small
A /24 gives 254 usable hosts, which is large enough

So the smallest valid subnet is:

/24

That means the calculator will divide the /16 into many /24 networks.

This is the classic exam pattern:

Find the smallest subnet that supports the required host count.

How to Think About Subnetting Quickly

Most subnetting questions can be solved with two rules:

Rule 1: More subnet bits = more subnets

If you borrow bits from the host portion:

you create more subnets
each subnet gets smaller

Formula:

2^(borrowed bits) = number of subnets

Rule 2: Fewer host bits = fewer usable hosts

Formula:

2^(host bits) - 2 = usable hosts

Example:

/24 leaves 8 host bits
2^8 = 256
256 - 2 = 254 usable hosts

That is why /24 supports 254 usable addresses in classic IPv4 subnetting.

Worked Example: Split a /24 into 8 Subnets

This is one of the most common subnetting practice questions.

Given:

Network: 192.168.0.0/24
Required subnets: 8

Step 1:

8 subnets requires 3 borrowed bits

Step 2:

/24 + 3 = /27

Step 3:

Each subnet increments by 32 addresses:

192.168.0.0/27
192.168.0.32/27
192.168.0.64/27
192.168.0.96/27
192.168.0.128/27
192.168.0.160/27
192.168.0.192/27
192.168.0.224/27

Each /27 subnet gives:

32 total IPs
30 usable hosts

That pattern is worth memorizing because it appears constantly in subnetting exercises.

Worked Example: Smallest Subnet for 50 Hosts

Given:

Host requirement: 50

You test common subnet sizes:

/27 = 30 usable hosts
/26 = 62 usable hosts

So the smallest valid subnet is:

/26

That means:

subnet mask = 255.255.255.192
block size = 64
usable hosts = 62

This is another very common certification-style subnetting pattern.

Subnetting Practice Tip

When practicing manually, remember this sequence:

Start with the original prefix.
Decide whether the problem is subnet-count-driven or host-count-driven.
Find the new prefix.
Calculate the block size.
List each subnet boundary.
Identify first usable, last usable, and broadcast.

The calculator above is useful both for solving the problem and checking your manual work after you finish.