Free CIDR to Subnet Mask & IPv4 Subnet Calculator

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Prefix / Subnet Mask
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Network Address
Broadcast Address
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Quick guide

What is IP subnetting?

IP subnetting is the process of breaking a large IP network into smaller, easier-to-manage segments. By creating these subnets, you can increase security, improve performance, and make more efficient use of IP addresses. Think of it as dividing a big office building into separate departments—each has its own area but remains part of the same structure.

Why should I subnet my network?

Security

Isolate sensitive systems and control how traffic moves between different parts of the network.

Performance

Cut down on broadcast traffic and reduce overall congestion to keep the network running smoothly.

Organization

Logically group devices by role, department, or location for cleaner network design.

Resource optimization

Distribute IP addresses efficiently so you only use what’s needed.

Network management

Make troubleshooting easier and apply access controls more effectively.

Free CIDR to Subnet Mask & IPv4 Subnet Calculator - What is IP subnetting?

What does CIDR mean?

CIDR stands for Classless Inter-Domain Routing. It replaced the old class-based system of IP addressing, allowing networks to be divided in a more flexible and efficient way.

CIDR notation looks like 192.168.1.0/24
192.168.1.0 → the base IP address
/ → the forward slash separator
24 → the prefix length, showing how many bits define the network portion

Free CIDR to Subnet Mask & IPv4 Subnet Calculator - What does CIDR mean?

Common CIDR notations and how they’re used

Different CIDR blocks define how many usable IP addresses are available within a subnet. Smaller ranges are typically used for point-to-point connections, while larger ranges power LANs, enterprise networks, and ISP allocations. Here are some common examples:

CIDR	Subnet Mask	Usable IPs	Typical Usage
`/32`	255.255.255.255	1	Single host (loopback or point-to-point)
`/30`	255.255.255.252	2	Router interconnects / point-to-point links
`/24`	255.255.255.0	254	Standard LAN or small office network
`/16`	255.255.0.0	65,534	Enterprise or large organization network
`/8`	255.0.0.0	16,777,214	ISP ranges / very large networks

What is my IP address?

Network address types made simple

Working with IP subnets involves different address types, each serving a specific role in routing and connectivity.

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Network address

The network address is always the first IP in a subnet. It identifies the subnet itself, with all host bits set to 0. For example, in 192.168.1.0/24, the network address is 192.168.1.0.

Broadcast address

The broadcast address is always the last IP in a subnet. It’s used to send data to all hosts within that network. All host bits are set to 1. For example, in the 192.168.1.0/24 subnet, the broadcast address is 192.168.1.255.

Usable host address

Host addresses are all the IPs between the network and broadcast addresses. These are assigned to devices within the subnet. In a /24 network, this gives you 254 usable IPs (256 total minus the network and broadcast addresses).

Subnetting in practice: examples and applications

Small office network (/24)

A common small office setup could use 192.168.1.0/24:

254 usable IP addresses
Simple subnet mask 255.255.255.0
Enough space for PCs, printers, and IoT devices

Department segregation (/25)

Dividing a /24 into two /25 networks:

Original: 192.168.1.0/24
Marketing: 192.168.1.0/25 (126 usable addresses)
Engineering: 192.168.1.128/25 (126 usable addresses)

Large campus network (/16)

A university network could use 172.16.0.0/16:

65,534 usable IP addresses
Plenty of room for future expansion
Easily subdivided into multiple smaller subnets

FAQ - IP subnet calculator

How do I choose the right subnet size for my network?

Keep these points in mind when sizing your subnets:

1. The number of devices you need to support today

2. Projected growth over the next 2–3 years (plan for 1.5–2× your current needs)

3. Segmentation needs such as security zones, departments, or services

4. Reserved IPs for infrastructure like routers, switches, and firewalls

For example, if you have 100 devices and expect 50% growth, a /24 (254 usable IPs) is safer than a /25 (126 usable IPs).

What’s the difference between a subnet mask and a wildcard mask?

Both are used to define network boundaries, but they serve different roles:

Subnet masks mark network bits with 1s and host bits with 0s (e.g., 255.255.255.0).

Wildcard masks invert that logic—0s for network bits and 1s for host bits (e.g., 0.0.0.255).

Wildcard masks are mainly used in access control lists (ACLs) and routing rules to decide which bits must match exactly and which can vary.

How do I prevent IP conflicts when subnetting?

Follow these best practices to avoid duplicate IPs:

Keep thorough documentation of all subnet allocations
Use a structured, hierarchical addressing plan
Leave buffer space between subnets for future growth
Adopt IP Address Management (IPAM) tools
Scan the network before rolling out new subnets
Use separate ranges for different sites or purposes

Can I merge subnets later if needed?

Yes, but only if the subnets are contiguous and properly aligned.

For example, two /25 networks (192.168.1.0/25 and 192.168.1.128/25) can be combined into a single /24.

Keep in mind:

1. The subnets must share the same parent block

2. All devices will need to be renumbered during consolidation

3. Careful subnet planning early on helps avoid the need for merging later

Which addresses should I always reserve in each subnet?

When planning, set aside these special addresses:

1. Network address – the first IP in the range

2. Broadcast address – the last IP in the range

3. Gateway address – usually the first or last usable IP

4. Infrastructure services – DHCP, DNS, NTP servers

5. Management IPs – for routers, switches, or firewalls

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IPv4 subnet calculator

Subnets

What is IP subnetting?

What does CIDR mean?

Common CIDR notations and how they’re used

Network address types made simple

Network address

Broadcast address

Usable host address

Subnetting in practice: examples and applications

Small office network (/24)

Department segregation (/25)

Large campus network (/16)

FAQ - IP subnet calculator

How do I choose the right subnet size for my network?

What’s the difference between a subnet mask and a wildcard mask?

How do I prevent IP conflicts when subnetting?

Can I merge subnets later if needed?

Which addresses should I always reserve in each subnet?

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IPv4 subnet calculator

Subnets

What is IP subnetting?

What does CIDR mean?

Common CIDR notations and how they’re used

Network address types made simple

Network address

Broadcast address

Usable host address

Subnetting in practice: examples and applications

Small office network (/24)

Department segregation (/25)

Large campus network (/16)

FAQ - IP subnet calculator

How do I choose the right subnet size for my network?

What’s the difference between a subnet mask and a wildcard mask?

How do I prevent IP conflicts when subnetting?

Can I merge subnets later if needed?

Which addresses should I always reserve in each subnet?

Launch today, risk-free for 30 days

Products

App hosting solutions

Features

Resources

Solutions by use case

Get help

Company

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