Subnet Mask Calculator & Complete Guide to Subnet Mask

In this guide, you will find the need for IP addressing (IPV4 and IPV6) in a networking and our online free subnet mask calculator will help to calculate IPv4 subnets.

In this tutorial, I’ve explained the significance of IP addressing, how subnet masking works with examples, and how to calculate an IP subnet mask manually and using a calculator. With this tutorial, you should be able to calculate and design your subnets nicely in any given networking configuration.

Our free subnet calculator for IPv4 and IPv6 will help for quick calculation of subnet masks, network address, broadcast address, host range, and other subnet information.

In our previous tutorials in the Complete Networking Training Series, we discussed LAN, WAN, and MAN in detail as these lessons will help to build the networking foundation. 

What is Subnet Mask

A subnet mask helps a computer or router understand which part of an IP address represents the network and which part represents the device (host).

Think of an IP address like a home address:

• The host part is like the house number.
• The network part is like the street name.

For example:

IP address: 192.168.1.25
Subnet mask: 255.255.255.0

The subnet mask tells us that the first 24 bits are used for the network, while the remaining 8 bits are available for hosts.

Example

For the network 192.168.1.0/24:

So, with an IP address such as 192.168.1.25/24:

• 192.168.1 → Network portion
• 25 → Host portion

The network is 192.168.1.0, and the usable host addresses are generally 192.168.1.1 to 192.168.1.254.

IP Address vs. Subnet Mask

IP Address	Subnet Mask
Identifies a specific device or network interface	Defines the boundary between the network and host portions
Example: 192.168.1.25	Example: 255.255.255.0
Usually different for each device on the same subnet	Usually the same for devices on the same subnet
Helps identify where a device is located on the network	Helps determine which part of the IP address represents the network and host

What Do 1s and 0s Mean in a Subnet Mask?

A subnet mask is made up of 32 binary bits, represented using 1s and 0s. These bits tell a computer or router which part of an IP address represents the network and which part represents the host (device).

• 1 = Network portion
• 0 = Host portion

Example: /24 Subnet Mask

Consider this subnet mask:

Dotted-decimal: 255.255.255.0
Binary: 11111111.11111111.11111111.00000000
CIDR: /24

Here is what the bits mean:

11111111.11111111.11111111.00000000

24 ones → Network bits
8 zeros → Host bits

So, if the IP address is:

192.168.1.25/24

the subnet mask tells the computer:

“The first 24 bits identify the network, and the last 8 bits identify the device.”

Another Simple Way to Understand It Think of the subnet mask as a boundary line:

11111111.11111111.11111111 | 00000000

Network portion | Host portion

For 192.168.1.25:

192.168.1 | 25

• 192.168.1 → Network
• 25 → Device/host

The 1s don’t mean “one device”, and the 0s don’t mean “zero devices.”

They simply indicate which bits belong to the network and which bits are available for identifying hosts.

How Does a Subnet Mask Work (IP Subnetting)

In our daily life, we human beings identify each other with our names; likewise, in computer networking, all network devices like routers, switches, etc., communicate with each other through an IP address and a subnet mask (Subnetting).

Subnetting is the backbone of efficient IP networking. In IPv4, we use subnet masks and network classes (A, B, C) to split big networks into smaller and manageable subnets. This helps in organizing devices, improving security, and making sure IP addresses are used wisely.

IPv6 takes a different approach — there are no classes or traditional subnet masks. Instead, subnetting is done using prefix lengths like /64 or /48, which makes the network more scalable and future-ready.

Whether you’re working with IPv4 or IPv6, understanding subnetting and using an IP subnet calculator can save you time and prevent errors when designing or troubleshooting a network.

The overall phenomenon of logical addressing works on the Layer-3 of the OSI reference model and the network components like routers and switches are the host devices that are most popularly used.

We will closely take a look at both IP versions in the following section:

Understanding Network Address and Host Address

An IPv4 Address is a 32-bit logical address that uniquely classifies a host on the network. The host can be a computer, a mobile handset or even a tablet. The 32-bit binary IP address is made up of two distinctive parts, i.e. The Network address and the Host address.

It also has 4 octets as each octet is having 8 bits. This octet is converted into decimal and is separated by a format i.e. dot. Thus it is represented in a dotted-decimal format. The range of an octet in binary is from 00000000 to 11111111 and in decimal from 0 to 255.

Example of an IPv4 Address format

192.168.1.64 (in decimal)

11000000.10101000.00000001.01000000 (in binary).

The binary one is difficult to memorize thus, in general, the dotted decimal format is used worldwide for representation of the logical addressing.

Let’s understand in detail how the binary octet values are converted into decimal values:

There are 8 bits and each bit has the value of 2 to the power n (2^n). The rightmost have the value 2^0 and left most have the value 2^7.

So the value of each bit is as follows:

2^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0 (^ denotes the power)

Thus the result would be:

128+ 64+ 32+ 16+ 8+ 4+ 2+ 1

When all the bits are 1 then the values come out to be 255 (128+64+32+16+8+4+2+1= 255).

Suppose all the bits of an octet is not 1. Then see how we can calculate the IP address:

1 0 0 1 0 0 0 1, 128+0+0+16+0+0+0+1= 145.

By combining the bits of the octets in different combinations according to the need, we can derive the overall IP address of the desired network. As per the requirement, these are divided into various classes of a network called as class A, class B, class C, class D, and class E.

Most popularly class A, B and C are used for commercial purposes and class D and E have reserved rights.

IPv4 Subnet Mask Cheat Sheet (/8 to /32)

CIDR	Subnet Mask	Total IPs	Usable IPs	Subnet Size
/8	255.0.0.0	16,777,216	16,777,214	16.7M
/9	255.128.0.0	8,388,608	8,388,606	8.4M
/10	255.192.0.0	4,194,304	4,194,302	4.2M
/11	255.224.0.0	2,097,152	2,097,150	2.1M
…	…	…	…	…
/23	255.255.254.0	512	510	512
/24	255.255.255.0	256	254	256
/25	255.255.255.128	128	126	128
/26	255.255.255.192	64	62	64
/27	255.255.255.224	32	30	32
/28	255.255.255.240	16	14	16
/29	255.255.255.248	8	6	8
/30	255.255.255.252	4	2*	4
/31	255.255.255.254	2	2*	2
/32	255.255.255.255	1	1*	1

Common Subnet Masks at a Glance

CIDR	Subnet Mask	Usable Hosts
/24	255.255.255.0	254
/25	255.255.255.128	126
/26	255.255.255.192	62
/27	255.255.255.224	30
/28	255.255.255.240	14
/29	255.255.255.248	6
/30	255.255.255.252	2

Free IP Subnet Calculator for IPv4 and IPv6

An IP Subnet Calculator automatically calculates and provides quick and error-free values of the broadcast IP address, usable IP range of the host devices, subnet mask, IP class and the total number of hosts by entering the subnet mask and the IP address of the particular network as the input values.

It is especially useful for beginners, large networks, or when you need fast results without doing binary calculations.

However, understanding manual subnet mask calculation is equally important. Calculating subnet masks manually helps you grasp how IP addressing, network bits, and host bits work together. This knowledge is essential for network design, troubleshooting connectivity issues, and preparing for certifications like CCNA or Network+.

Why Do You Need an IP Calculator?

An IP calculator is beneficial in easily computing key parameters in the network, such as the network address, the first IP address available for use, the last IP address available for use, the broadcast address, number of subnets, and number of usable hosts.

The above computations may be done manually using the help of subnetting formulas and binary computation. But when dealing with large networks or several subnets, manual computation becomes difficult and increases chances of mistakes.

Let us see the importance of an IP calculator with a couple of examples.

Example 1: Calculating a /28 Subnet

Consider the following network:

• IP address: 190.164.24.0
• Subnet mask: 255.255.255.240
• CIDR notation: /28

The subnet mask in binary is:

11111111.11111111.11111111.11110000

Here, 4 bits are borrowed from the host portion for subnetting.

Number of subnets = 2⁴ = 16

Number of addresses per subnet = 2⁴ = 16

Usable host addresses per subnet = 2⁴ – 2 = 14

For the network 190.164.24.0/28, the first subnet has:

All these ranges share the same subnet mask: 255.255.255.240 (/28).

Doing all these network range calculations using manual methods involves doing some binary and mathematical calculations. But this process can be simplified by an IP calculator.

Example 2: Calculating a Large Network

Consider the following Class A private network:

• IP address: 10.0.0.0
• Subnet mask: 255.252.0.0
• CIDR notation: /14

With a /14 subnet mask:

• Total addresses per subnet: 2¹⁸ = 262,144
• Usable host addresses: 262,144 – 2 = 262,142
• Number of /14 networks within a /8: 2⁶ = 64

Network range and host address calculation can be quite complex for such a big network.

This is where a IP calculator or subnet calculator can be of great use. The calculator automatically calculates all the required parameters of the network using the IP address and subnet mask input by the user.

Such a IP subnet Calculator tool helps to determine:

• Network address
• Broadcast address
• First usable IP address
• Last usable IP address
• Number of subnets
• Number of usable hosts
• Host range
• CIDR notation
• Subnet mask

The results are generated quickly and reduce the possibility of calculation errors. This is particularly useful when designing or dividing large networks into smaller subnets.

Example 3: Calculating a /18 Subnet

Consider another network:

• IP address: 10.0.0.0
• Subnet mask: 255.255.192.0
• CIDR notation: /18

For a /18 network:

• Total addresses per subnet: 2¹⁴ = 16,384
• Usable host addresses: 16,384 – 2 = 16,382
• Number of /18 subnets within a /8: 2¹⁰ = 1,024

Performing calculations for the network address, broadcast address, host range, etc., can be quite time-consuming.

IP Calculator does this automatically and presents the output in an easy-to-understand manner.

For large networks, the program can save a lot of time and help network administrators and developers to do their work more effectively.

Thus with the help of the above examples, we can get the subnet details as per our requirements.

The below table demonstrates the various IPV4 subnet details:

What is IPv6, How it works and its Subnetting

While IPv4 uses network classes (A, B, C) and subnet masks to divide networks, IPv6 does not use classes at all. Instead, IPv6 uses a prefix length to define the network portion of an address because IPv6 addresses are 128 bits long rather than 32 bits like IPv4.

In IPv6:

• There is no Class A/B/C/D/E division of addresses like in IPv4.
• Subnetting is done using CIDR-style prefixes (e.g., /64, /56, /48).
• A standard IPv6 subnet uses a /64 prefix, meaning the first 64 bits are the network portion and the remaining 64 bits are for interface (host) IDs.

IPv6 Subnet Structure

An IPv6 address consists of:

1. Global routing prefix – Assigned by an ISP
2. Subnet ID – Used to create subnets within an organization
3. Interface ID – Identifies individual hosts on the subnet

A typical IPv6 subnet looks like: 2001:db8:abcd:0012::/64

Here, /64 tells the router how many bits define the subnet.

Why /64 Is Common

Although IPv6 can use other prefix lengths, /64 is the recommended and most common subnet size because:

• It supports automatic address configuration (SLAAC) for devices.
• It gives every subnet a huge number of possible addresses (2^64).

IPv4 vs IPv6 Subnetting

Feature	IPv4	IPv6
Address Length	32 bits	128 bits
Uses Classes?	Yes (A/B/C)	No
Subnet Mask	Dotted decimal	Only prefix length
Typical Subnet	/24	/64

/29 Subnet Mask Explained

/29 subnet mask is among the widely adopted small subnets of network for IPv4 networking. This subnet offers a concise number of IP addresses that can be utilized to link a few devices without having to waste IP addresses. Networks with /29 subnet masks are normally deployed to connect WAN links, small offices, firewalls, routers, and cloud networking environments.

What Is a /29 Subnet?

CIDR notation with /29 indicates that 29 out of 32 bits are dedicated to the network part of the address. This leaves three bits that can be used by host addresses.

A /29 address provides a small-sized subnet with:

• 8 total IP addresses
• 6 host addresses
• 1 network address
• 1 broadcast address

Given there are just three host bits left, the /29 subnet will work well if only a few devices have to use IP addresses.

/29 Subnet Mask in Decimal

The decimal subnet mask for a /29 subnet is:

255.255.255.248

Binary representation:

11111111.11111111.11111111.11111000

The final octet contains 29 network bits and 3 host bits.

CIDR Prefix	Subnet Mask	Total Addresses	Usable Hosts
/29	255.255.255.248	8	6

Number of Hosts in a /29 Network

To calculate usable hosts, use the standard subnetting formula:

Address Type	Count
Total IP Addresses	8
Network Address	1
Broadcast Address	1
Usable Host Addresses	6

It simply implies that the maximum number of devices like servers, routers, firewalls, switches, or even virtual machines supported by a /29 subnet is six.

/29 Example Calculation

Suppose the assigned subnet is:

192.168.10.0/29

Item	Value
Network Address	192.168.10.0
First Usable Host	192.168.10.1
Last Usable Host	192.168.10.6
Broadcast Address	192.168.10.7
Usable Hosts	6

Quick Answer: A /29 subnet (subnet mask = 255.255.255.248) contains a total of eight IP addresses but six usable ones, making it perfect for smaller networks, IP assignments, and point-to-point network infrastructures that need a few devices.

Understanding IP Network Classes and Subnet Masks (A, B, C, D, E)

The organization which governs the internet has divided the IP addresses into different classes of the network.

Each class is identified by its subnet mask. By the categorization of a default subnet mask, we can easily identify the class of an IP address of the network. The first octet of an IP address identifies the particular class of an IP address.

The classification is shown with the help of the below table and figure.

• The class ‘A’ Address ranging from 127.0.0.0 to 127.255.255.255 cannot be used and is reserved for loopback and diagnostic functions. The numbers of hosts which can be connected to this network are greater than 65536 hosts.
• The number of hosts connected within the class B networks is from 256 to 65534 hosts.
• The number of hosts connected within the class C network is less than 254 hosts. Therefore the class C network mask is perfect for the minor networks which are known as subnetworks. We utilize the bits from the last octet of class C for constructing mask. Thus we need to rearrange and optimize the subnet depending upon the availability of the bits.

Below table will show the masks that can be drawn on with Class C networks.

We have studied about the network class and subnet mask phenomenon of computer networking. Now let’s see how the mask will help us to classify the network ID and host ID part of an IP address.

Let us assume the case of a class A IP address:

For Example, take a pair of IP address and subnet mask 10.20.12.2 255.0.0.0

#1) Convert this Combination into a binary value:

#2) The bits corresponding to the subnet mask with all 1’s represent the network ID as it is a class A network and the first octet represents the network ID. The bits corresponding to all 0’s of the subnet mask is the host ID. Thus the network ID is 10 and the host ID is 20.12.2

#3) From the given subnet, we can also calculate the IP range of a particular network. If the IP is 10.68.37.128 (assuming class A case)

Subnet mask: 255.255.255.224
IP range =256-224= 32.
Out of 32 IP’s, ideally one is used for the gateway, second is for the network IP and the third is for broadcast IP.
Thus total usable IP’s are 32-3= 29 IP’s.

The IP range will be 10.68.27.129 to 10.68.27.158.

Subnet Mask Notation Explained: Decimal, Binary, and CIDR

Subnetting allows us to create various sub-networks or logical networks within one network of a particular class of the network. Without subnetting, it is almost unrealistic to create big networks.

For constructing a big networking system, every link must have a unique IP address with every device on that linked network which is being the participant of that network.

With the help of a subnetting technique, we can split the large networks of a particular class (A, B or C) into smaller subnetworks for inter-connection between each node which are situated at different locations.

Each node on the network would have a distinctive IP and subnet mask IP. Any switch, router or gateway that connects n networks has n unique Network ID and one subnet mask for each of the network it interconnects with.

The formulae of subnetting is as follows:

2^n >= requirement.

The formulae of a number of hosts per subnet is as follows:

2^n -2

Now let’s understand the overall process with the help of an Example:

We have taken an example of Class C network ID with a default subnet mask.

Suppose Network ID/IP address is: 192.168.1.0

Default Subnet mask: 255.255.255.0 (in decimal)

Default Subnet mask: 11111111.11111111.11111111.00000000 (in binary)

Thus the number of bits are 8+8+8+0= 24 bits. As mentioned earlier, for subnetting in class C network, we will borrow bits from the host portion of the subnet mask.

Therefore, to customize the subnet as per requirement:

We take a subnet mask of 255.255.255.248 (in decimal)

11111111.11111111.11111111.11111000 (in binary).

From the above binary notation, we can see that the last 3 bits of the last octet can be used for host ID addressing purpose.

Thus the number of subnets= 2^n = 2^3= 8 subnets (n=3).

Number of hosts per subnet= 2^n -2= 2^3 -2= 8-2= 6 Subnets i.e. usable Host IP.

Now the IP addressing scheme is as follows:

The subnet mask for all the above IP’s in the table is common i.e. 255.255.255.248.

With the help of the above example, we can clearly see, how subnetting helps us to construct inter-networking between various links and nodes of the same subnetwork. All these above IP’s can be used for inter-networking the devices within the overall network.

Note: Subnet mask is most widely used everywhere in a computer networking system. Hence, there is one more method to represent the subnet mask of a particular network which is chosen and standardized as it is easy to denote and memorize.

Subnet mask– 255.255.255.248 (binary)

11111111.11111111.11111111.11111000 (decimal notation)

From the decimal notation we can calculate the number of bits having 1 in each octet:

8+8+8+5= 29

Thus the Subnet mask can be denoted as /29.

With Network ID it can be denoted as 192.168.1.9/29.

From the above notation, anyone who knows the standard notation and formulae of subnetting can understand that the IP is using a subnet mask of 255.255.255.248 or /29.

The different Subnetting scheme in binary and decimal notation is shown below:

The ‘/’ notation method of the subnet mask is most widely used as it is easy to memorize and the binary notation and decimal are very lengthy in size.

As we are denoting the mask scheme while interconnecting the network components through the figure, if we use the decimal and binary method then the overall diagram will become very complex and difficult to understand.

There are so many IP’s on the platform to be shown and it becomes difficult to memorize as well. Thus generally, people who are familiar with routing and IP addressing scheme use short notation methods in figures and diagrams.

Example 1:

Understanding Subnetting with an Example of Interconnection of Network Devices:

The above figure shows how subnetting is used for interconnection of subnetworks. Firstly, as per our need for the number of hosts required to be connected and meet the other requirements of the network, we customize the subnet mask and network ID accordingly and assign to the devices thereafter.

The above network is using class C network mask and /29 subnet mask means network IP can be divided into 8 subnets. Each router has a unique IP address for each linked subnetwork.

There is an important point to be noticed that the more the bits we carry from the subnet mask for host ID then the more will be the subnets obtainable for the network.

Example 2:

Class B Network:

The above table shows the details of the number of subnets and hosts that can be connected per subnet mask by using Class B subnetting Scheme.

For connecting a host in big quantity and WAN communication systems, the Class B subnetting is very effective as it gives a wide range of IP’s for configuration.

=> Watch Out The Simple Computer Networking Basics

Frequently Asked Questions about IP Subnetting

Conclusion

In this tutorial, we have learned the need for IP addressing and Subnetting in the computer networking systems, with the help of different examples.

The IP addressing scheme and Subnetting are the building blocks in defining the subnetworks and IP’s within a large network.

The different formulas we have used will help us in determining the hosts that we can connect in a particular network and how also enable us to know how a huge network can be divided into many smaller networks for easier communication.

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