IP Subnet Calculator

Enter an IPv4 address and either a prefix (e.g. /24) or a subnet mask (e.g. 255.255.255.0). The calculator shows network info and usable hosts.

IPv4 Address

Prefix / Mask

Calculate Reset

Subnet Information

Copy

Notes: This tool handles IPv4 only. Usable host counts follow conventional rules (for /31 and /32 it reports total addresses and RFC-3021 note for /31).

IP Subnet Calculator Online – Calculate Subnets Easily

Intro

Managing IP addresses is one of the most important tasks in computer networking. Whether you are a network administrator, IT professional, or student, understanding how to divide an IP address into subnets can be confusing. This is where an IP Subnet Calculator online becomes extremely useful.

An IP Subnet Calculator helps you quickly determine subnet masks, network addresses, broadcast addresses, and the number of valid hosts within a subnet. Instead of doing long binary calculations by hand, this tool provides instant and accurate results, saving time and reducing errors.

Anyone working with IPv4 or IPv6 networks, from small office setups to large enterprise systems, can benefit from this calculator. It’s simple, accurate, and designed for both learning and professional use.

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Formula / Working

Subnetting works by dividing an IP address into network bits and host bits.

Key Formulas:

1. Number of subnets:

2n2^n2n

where n = number of borrowed bits.

2. Number of hosts per subnet:

2h−22^h – 22h−2

where h = number of host bits (subtract 2 for network and broadcast addresses).

3. Subnet mask representation:
   For IPv4, a subnet mask is shown as /CIDR notation. Example: /24 = 255.255.255.0.

Example Formula Breakdown:

• IP: 192.168.1.0/26
• Subnet mask: 255.255.255.192
• Borrowed bits: 2
• Subnets: 22=42^2 = 422=4
• Hosts per subnet: 26−2=622^6 – 2 = 6226−2=62

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Step-by-Step Usage

Using the IP Subnet Calculator online is easy:

1. Enter the IP address (e.g., 192.168.1.1).
2. Select the subnet mask or CIDR value (e.g., /24).
3. Click “Calculate.”
4. The tool will instantly show:
   • Network address
   • Broadcast address
   • Subnet mask in dotted-decimal
   • Number of usable hosts
   • First and last usable IP

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Examples

Example 1 – Subnetting a /24 Network

• Input: 192.168.1.0/24
• Output:
  • Subnet mask: 255.255.255.0
  • Usable hosts: 254
  • Network address: 192.168.1.0
  • Broadcast address: 192.168.1.255

Example 2 – Splitting into /26 Subnets

• Input: 192.168.1.0/26
• Output for one subnet:
  • Subnet mask: 255.255.255.192
  • Usable hosts: 62
  • Network address: 192.168.1.0
  • Broadcast address: 192.168.1.63

Example 3 – IPv6 Subnetting

• Input: 2001:db8::/64
• Output:
  • Subnet mask: /64
  • Possible subnets: billions (since IPv6 has massive address space)
  • First usable address: 2001:db8::1

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FAQs

1. What is an IP Subnet Calculator?
It’s an online tool that calculates network, broadcast, and host ranges based on an IP address and subnet mask.

2. Does it work for both IPv4 and IPv6?
Yes, most calculators support both IPv4 and IPv6 subnetting.

3. Why do I need subnetting?
Subnetting helps organize networks, improve security, and efficiently use IP addresses.

4. How many hosts can a /30 subnet support?
A /30 provides 2 usable host addresses (suitable for point-to-point links).

5. What is the difference between /24 and /16?

• /24 = 254 usable hosts
• /16 = 65,534 usable hosts