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IP Subnet Calculator

Calculate subnet properties including network address, broadcast address, and usable host range from a CIDR prefix length.

Reviewed by Christopher FloiedPublished Updated

This free online ip subnet calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

Range: 1 – 32

Subnet mask prefix length (1-32)

Results

Total Addresses

256

Usable Host Addresses

254

Host Bits

8

How to Use This Calculator

1

Enter your input values

Fill in all required input fields for the IP Subnet Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

2

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

3

Read the results

The IP Subnet Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

4

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

Formula Reference

IP Subnet Calculator Formula

See calculator inputs for the governing equation

Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.

When to Use This Calculator

  • •Use the IP Subnet Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
  • •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
  • •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
  • •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

About This Calculator

The IP Subnet Calculator is a free, browser-based calculation tool for engineers, students, and technical professionals. Calculate subnet properties including network address, broadcast address, and usable host range from a CIDR prefix length. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.

About IP Subnet Calculator

The IP Subnet Calculator computes subnet properties from a CIDR prefix length. Subnetting is a fundamental networking concept used to divide large networks into smaller, more manageable segments. This calculator shows the total number of addresses, usable host addresses, and host bits for any subnet size, helping network administrators plan IP address allocation and design efficient network architectures.

The Math Behind It

IPv4 addresses are 32-bit numbers divided into a network portion and a host portion by a subnet mask. The CIDR (Classless Inter-Domain Routing) notation uses a prefix length to indicate how many bits belong to the network portion. For example, /24 means 24 network bits and 8 host bits. The number of total addresses in a subnet is 2 raised to the power of the host bits (32 minus the prefix length). A /24 subnet has 2^8 = 256 total addresses. However, two addresses are reserved: the network address (all host bits set to 0) and the broadcast address (all host bits set to 1). Therefore, usable host addresses equal total addresses minus 2. Common subnet sizes include: /32 (single host), /30 (4 addresses, 2 usable, for point-to-point links), /24 (256 addresses, 254 usable, the classic Class C), /16 (65,536 addresses), and /8 (16.7 million addresses). Subnetting serves several purposes: reducing broadcast domain size for better network performance, improving security by isolating network segments, efficient use of IP address space, and meeting organizational requirements for network separation. VLSM (Variable Length Subnet Masking) allows different subnets to have different sizes within the same network, optimizing address usage. For example, a server VLAN might use a /24 while a point-to-point link uses a /30. When designing subnets, always plan for growth. Choosing a subnet size that exactly matches current needs leaves no room for additional hosts. It is common practice to allocate subnets at least twice the size of current requirements.

Formula Reference

Subnet Size

Total Addresses = 2^(32 - prefix), Usable = Total - 2

Variables: prefix = CIDR prefix length (e.g., 24 for /24), subtract 2 for network and broadcast addresses

Worked Examples

Example 1: Office network subnet planning

Plan a /24 subnet for an office network.

Step 1:Host bits: 32 - 24 = 8
Step 2:Total addresses: 2^8 = 256
Step 3:Usable hosts: 256 - 2 = 254
Step 4:Network address: .0 (reserved)
Step 5:Broadcast address: .255 (reserved)

A /24 subnet provides 254 usable IP addresses, suitable for a small to medium office.

Common Mistakes & Tips

  • !Forgetting to subtract 2 from the total for network and broadcast addresses.
  • !Confusing CIDR prefix length with the number of host bits (they are complementary, summing to 32).
  • !Not planning for growth by choosing a subnet size that exactly matches current needs.

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Frequently Asked Questions

What is the most common subnet size?

The /24 subnet (256 addresses, 254 usable) is the most widely used for local area networks. It provides enough addresses for most small to medium networks while keeping the broadcast domain manageable.

What is the difference between /24 and 255.255.255.0?

They mean the same thing. /24 is CIDR notation indicating 24 network bits. 255.255.255.0 is the dotted-decimal subnet mask form. Both leave 8 bits for host addresses.