What is a subnet calculator used for?

A subnet calculator is used to determine network information from an IP address and subnet mask. It calculates the network address, broadcast address, usable IP range, number of available hosts, and helps network administrators plan and organize IP address allocation efficiently.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its subnet mask. It uses a slash followed by a number (e.g., /24) indicating how many bits are used for the network portion. For example, 192.168.1.0/24 means the first 24 bits are the network address.

How do I calculate the number of usable hosts in a subnet?

The number of usable hosts is calculated using the formula: 2^(32-prefix) - 2. The subtraction of 2 accounts for the network address and broadcast address which cannot be assigned to hosts. For example, a /24 subnet has 2^8 - 2 = 254 usable hosts. A /31 subnet has 2 usable hosts (point-to-point links) and a /32 represents a single host.

What are private IP address ranges?

Private IP address ranges are reserved for internal networks and include: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255), 172.16.0.0/12 (172.16.0.0 to 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 to 192.168.255.255). These addresses are not routable on the public internet.

Is this subnet calculator really free?

Yes! This subnet calculator is completely free to use with no subscriptions, registrations, or hidden fees. FreeWWW.com provides free tools and utilities for everyone. Calculate unlimited subnets without any cost or limitations.

Free Online Subnet Calculator (No Signup)

About This Tool

Enter an IP address and subnet mask to instantly see the network address, broadcast address, usable host range, host counts, wildcard mask, class and a binary breakdown. Split networks into equal subnets, plan variable-size subnets with VLSM, check whether an IP falls inside a subnet, and calculate IPv6 prefixes. Everything runs in your browser — nothing is uploaded.

How to Use This Tool

Enter an IP address — Type an IPv4 address (e.g., 192.168.1.0) in the IP Address field
Set the subnet mask — Enter a subnet mask (e.g., 255.255.255.0) or CIDR notation (e.g., /24), or use the slider for quick selection
Use quick presets — Click preset buttons like /8, /16, /24 to jump to common subnet sizes
Review the results — See network address, broadcast address, usable host range, host counts, wildcard mask and a binary breakdown instantly
Explore the tabs — Use the Subnet Divider, VLSM Planner, IP-in-Subnet check, and IPv6 calculator for advanced tasks

Common Use Cases

How many usable hosts are in a /24 subnet? Enter any IP with /24 to instantly see the host count, network range, and broadcast address
How do I convert a subnet mask to CIDR notation? Enter the subnet mask (e.g., 255.255.255.128) and the tool shows the equivalent CIDR prefix length
Is an IP inside a given subnet? Use the IP-in-Subnet tab to test membership for ACLs and firewall rules
How do I plan unequal subnets? Use the VLSM Planner to fit host requirements into the smallest possible subnets

Network Information

Network Address

Broadcast Address

First Usable Host

Last Usable Host

Subnet Mask

CIDR Notation

Total Addresses

Usable Hosts

Network Class

IP Type

Wildcard Mask

Reverse DNS (in-addr.arpa)

Host Capacity

Usable hosts

Network & broadcast (reserved)

Binary Breakdown

Blue bits are the network portion, orange bits are the host portion.

Subnet Divider

Split the network above into equal-sized smaller subnets.

Number of Subnets to Create:

VLSM Planner

Enter required host counts (one per line) and we fit each into the smallest subnet of the network above, largest first.

Hosts required per subnet (one number per line):

IP-in-Subnet Check

Check whether an IP address belongs to the network above.

IP Address to Test:

IPv6 Prefix Calculator

Enter an IPv6 address and prefix length.

IPv6 Address:

Prefix Length: /64

Recent Calculations

Click an entry to reload it. Stored locally in your browser.

🌐 Subnet Calculator