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Subnet Calculator

Calculate CIDR, subnet masks, and address ranges.

Formula Verified by Dr. James Callahan, PhD

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

Octet 1

Octet 2

Octet 3

Octet 4

CIDR prefix

Results

Network address

192.168.1.0/24

Subnet mask255.255.255.0

Broadcast192.168.1.255

Usable hosts254

Host range192.168.1.1 - 192.168.1.254

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Keep this network calculator handy for IP addressing, routing setup, or certification study.

Formula

Subnet calculation

Network = IP AND subnet mask; Broadcast = network OR inverted mask

The calculator converts the IPv4 address into a 32-bit integer, applies the CIDR mask, and derives the network, broadcast, and host range.

Step by step

How the calculation works

1Enter the four IPv4 octets and the CIDR prefix.
2Build the subnet mask from the prefix length.
3Apply bitwise masking to derive the network address.
4Use the remaining host space to estimate the broadcast address and usable range.

Example

Example subnet result

192.168.1.10/24 belongs to the 192.168.1.0/24 network with 254 usable host addresses.

Related guides

Learn more about this calculation

Guide

IPv4 Subnetting Basics: CIDR, Masks, and Hosts

Learn IPv4 subnetting with a clear /26 example: convert CIDR to a mask, find block boundaries, and calculate network, broadcast, and host ranges.

Guide

Scientific Notation Guide: Powers of Ten Made Practical

Learn how to convert, compare, and calculate with powers of ten using worked examples and the live DTC scientific calculator.

How to understand and use this calculator

Subnetting and Network Design Principles

Subnetting is the practice of dividing a single large physical network into multiple smaller, logical subnetworks (subnets). This division is a fundamental building block of IP networking, helping to reduce broadcast storm traffic, isolate security zones, and optimize routing efficiency.

Every IPv4 address consists of two parts: the network portion (used by routers to locate the subnet) and the host portion (used to locate the specific device on that subnet). The Subnet Mask determines exactly where this split occurs.

Bitwise Masking Mathematics

To calculate subnet boundaries, networking hardware performs bitwise operations on the 32-bit binary representations of the IP address and the subnet mask.

Network Address: Calculated by performing a bitwise AND operation between the IP address and the subnet mask:

$$\text{Network Address} = \text{IP Address} \text{ AND } \text{Subnet Mask}$$

Broadcast Address: Calculated by setting all host bits of the network address to binary 1:

$$\text{Broadcast Address} = \text{Network Address} \text{ OR } (\text{NOT } \text{Subnet Mask})$$

Usable Host Range: The IPs sitting strictly between the Network Address and the Broadcast Address. The host capacity is $2^{(32 - ext{CIDR})} - 2$. We subtract 2 because the network address (first IP) and the broadcast address (last IP) are reserved and cannot be assigned to devices.

CIDR Notation and Prefix Lengths

Classless Inter-Domain Routing (CIDR) notation expresses the subnet mask size as a slash followed by the count of leading binary 1s (network bits). For example, a `/24` prefix represents a mask with 24 leading 1s: `255.255.255.0`. This mask leaves 8 bits for hosts, supporting $2^8 - 2 = 254$ usable devices.

For controlling traffic density and request flow across your subnet boundaries, you will need a robust rate limiting system. Model your request limits with our API Rate Limiting & Token Bucket Simulator.

Related concepts

CIDR notation

Classless Inter-Domain Routing notation, which specifies network prefix length (e.g., /24) to define mask size.

Broadcast address

An IP address used to target all hosts on a subnet simultaneously.

Default Gateway

The router IP that forwards local traffic outside the local subnet.

Frequently Asked Questions

Why are the first and last host IP addresses reserved?+

The first address in a subnet is reserved for the network address itself, and the last address is reserved for the broadcast address. Usable host IPs sit between these boundaries.

What is a subnet mask?+

A 32-bit number that hides or masks the host portion of an IP address, leaving only the network portion visible to routing protocols.

What is CIDR notation?+

Classless Inter-Domain Routing notation, which specifies network prefix length (e.g., /24) to define mask size.

How many usable hosts are in a /24 subnet?+

A /24 subnet has 8 host bits, yielding 256 total addresses. Subtracting the network and broadcast addresses leaves 254 usable host IPs.

What is a broadcast address?+

An IP address used to target all hosts on a subnet simultaneously.

How does bitwise AND work in subnetting?+

The calculator compares the binary bits of the IP and mask. If both are 1, the result is 1; otherwise, it is 0, revealing the base network address.

What is the purpose of subnetting?+

Subnetting improves security, limits broadcast traffic, and organizes network devices into logical groups (e.g., separating guest WiFi from server networks).

What is a default gateway?+

A router interface that connects the local subnet to other networks. It typically takes the first or last usable IP address in the subnet.

What is a Class A, B, and C network?+

Historical legacy IP classifications: Class A (/8) for large networks, Class B (/16) for medium networks, and Class C (/24) for local networks, now replaced by CIDR.

How do I divide a /24 subnet into two smaller networks?+

Increase the prefix length by 1 bit to /25. This creates two subnets with 128 total addresses (126 usable hosts) each.

How to understand and use this calculator

Subnetting and Network Design Principles

Bitwise Masking Mathematics

To calculate subnet boundaries, networking hardware performs bitwise operations on the 32-bit binary representations of the IP address and the subnet mask.

Network Address: Calculated by performing a bitwise AND operation between the IP address and the subnet mask:

$$\text{Network Address} = \text{IP Address} \text{ AND } \text{Subnet Mask}$$

Broadcast Address: Calculated by setting all host bits of the network address to binary 1:

$$\text{Broadcast Address} = \text{Network Address} \text{ OR } (\text{NOT } \text{Subnet Mask})$$

CIDR Notation and Prefix Lengths

Related concepts

CIDR notation

Classless Inter-Domain Routing notation, which specifies network prefix length (e.g., /24) to define mask size.

Broadcast address

An IP address used to target all hosts on a subnet simultaneously.

Default Gateway

The router IP that forwards local traffic outside the local subnet.

Frequently Asked Questions

Why are the first and last host IP addresses reserved?+

The first address in a subnet is reserved for the network address itself, and the last address is reserved for the broadcast address. Usable host IPs sit between these boundaries.

What is a subnet mask?+

A 32-bit number that hides or masks the host portion of an IP address, leaving only the network portion visible to routing protocols.

What is CIDR notation?+

Classless Inter-Domain Routing notation, which specifies network prefix length (e.g., /24) to define mask size.

How many usable hosts are in a /24 subnet?+

A /24 subnet has 8 host bits, yielding 256 total addresses. Subtracting the network and broadcast addresses leaves 254 usable host IPs.

What is a broadcast address?+

An IP address used to target all hosts on a subnet simultaneously.

How does bitwise AND work in subnetting?+

The calculator compares the binary bits of the IP and mask. If both are 1, the result is 1; otherwise, it is 0, revealing the base network address.

What is the purpose of subnetting?+

Subnetting improves security, limits broadcast traffic, and organizes network devices into logical groups (e.g., separating guest WiFi from server networks).

What is a default gateway?+

A router interface that connects the local subnet to other networks. It typically takes the first or last usable IP address in the subnet.

What is a Class A, B, and C network?+

Historical legacy IP classifications: Class A (/8) for large networks, Class B (/16) for medium networks, and Class C (/24) for local networks, now replaced by CIDR.

How do I divide a /24 subnet into two smaller networks?+

Increase the prefix length by 1 bit to /25. This creates two subnets with 128 total addresses (126 usable hosts) each.

Subnet Calculator

Inputs

Results

Bookmark this subnet tool

Subnet calculation

How the calculation works

Example subnet result

Learn more about this calculation

IPv4 Subnetting Basics: CIDR, Masks, and Hosts

Scientific Notation Guide: Powers of Ten Made Practical

Subnet Calculator

Inputs

Results

Bookmark this subnet tool

Key output metrics

IP Address Octets

Capacity Prefix (CIDR)

How to understand and use this calculator

Subnetting and Network Design Principles

Bitwise Masking Mathematics

CIDR Notation and Prefix Lengths

Related concepts

Frequently Asked Questions

Subnet calculation

How the calculation works

Example subnet result

Learn more about this calculation

IPv4 Subnetting Basics: CIDR, Masks, and Hosts

Scientific Notation Guide: Powers of Ten Made Practical

Key output metrics

IP Address Octets

Capacity Prefix (CIDR)

How to understand and use this calculator

Subnetting and Network Design Principles

Bitwise Masking Mathematics

CIDR Notation and Prefix Lengths

Related concepts

Frequently Asked Questions