VLSM (Variable Length Subnet Masking) allows dividing a network into subnets of different sizes. Instead of using one fixed subnet mask, VLSM optimizes IP address usage by allocating exactly the number of addresses each subnet needs.

How many usable hosts in a /24 subnet?

A /24 subnet has 256 total addresses (2^8). Subtract 2 for the network and broadcast addresses, giving 254 usable host addresses. This calculator shows usable hosts for any CIDR prefix.

Does this subnet calculator support IPv6?

Yes. Enter an IPv6 address with a prefix length (e.g. 2001:db8::/32) to calculate the network range, total addresses, and prefix details for IPv6 subnets.

What is a /32 subnet?

A /32 subnet contains exactly one IP address. It is commonly used for host routes in routing tables and loopback interfaces. The subnet mask is 255.255.255.255.

Free Subnet Calculator — IPv4/IPv6 CIDR, VLSM, Wildcard Mask & Network Planner Online

Frequently Asked Questions — Subnet Calculator

What is a subnet calculator?

A subnet calculator computes network details from an IP address and CIDR prefix or subnet mask. It calculates the network address, broadcast address, subnet mask, wildcard mask, usable host range, and total number of hosts in the subnet. This tool does all calculations instantly in your browser.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its routing prefix. For example, 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits (256 addresses) for hosts. CIDR replaced the old classful addressing system (Class A/B/C) in 1993.

How do I calculate a subnet mask from CIDR?

Convert the CIDR prefix to binary: set the first N bits to 1 and the rest to 0. For /24: 11111111.11111111.11111111.00000000 = 255.255.255.0. For /20: 11111111.11111111.11110000.00000000 = 255.255.240.0. This calculator does the conversion instantly.

What is a wildcard mask?

A wildcard mask is the inverse of a subnet mask — it flips all bits. For subnet mask 255.255.255.0, the wildcard is 0.0.0.255. Wildcard masks are used in Cisco ACLs, OSPF area definitions, and other network device configurations where you need to specify which bits to match.

What is VLSM and why should I use it?

VLSM (Variable Length Subnet Masking) allows dividing a network into subnets of different sizes. Instead of wasting addresses with one fixed subnet size, VLSM allocates exactly the right number of addresses each subnet needs — saving IP space and making network planning more efficient.

How many usable hosts are in a /24 subnet?

A /24 subnet has 256 total addresses (2^8). Subtract 2 for the network address and broadcast address, giving 254 usable host addresses. The formula is: usable hosts = 2^(32 - prefix) - 2. For /24: 2^8 - 2 = 254.

What is the difference between network and broadcast address?

The network address is the first address in a subnet (all host bits = 0) and identifies the network itself. The broadcast address is the last address (all host bits = 1) and is used to send data to all hosts. Neither can be assigned to a device.

Does this calculator support IPv6?

Yes. Switch to the IPv6 tab and enter any IPv6 address with a prefix length (e.g. 2001:db8::/32). The calculator shows the expanded address, network prefix, total addresses, and full address range.

What are private IP address ranges?

RFC 1918 defines three private ranges: 10.0.0.0/8 (Class A — 16M addresses), 172.16.0.0/12 (Class B — 1M addresses), and 192.168.0.0/16 (Class C — 65K addresses). These are not routed on the public internet and are used for internal networks.

Is this subnet calculator free to use?

Yes, completely free with no limits, no signup, and no ads. All calculations run 100% in your browser — no data is sent to any server. It is one of 48 free tools at jasperbernaers.com.

Free Online Subnet Calculator — IPv4/IPv6 CIDR, VLSM & Network Planning

This free subnet calculator instantly computes all subnet details from any IPv4 or IPv6 address with CIDR prefix. Whether you're a network engineer, sysadmin, CCNA student, or cloud architect, get instant answers for subnet masks, wildcard masks, network and broadcast addresses, usable host ranges, and binary breakdowns.

Subnet Calculator Features

▸ IPv4 Subnet Calculator — enter any IP address with CIDR prefix (/0 to /32) for instant network details
▸ VLSM Planner — divide networks into variable-length subnets, optimizing IP address allocation
▸ CIDR Cheat Sheet — complete reference table of all 33 prefix lengths with masks and host counts
▸ IPv6 Calculator — full IPv6 address expansion and prefix calculation
▸ Binary Breakdown — visual binary representation showing network vs host bits
▸ IP Classification — automatic detection of IP class (A/B/C/D/E), private vs public, and special ranges

Who Uses a Subnet Calculator?

Network engineers, system administrators, DevOps teams, cloud architects, CCNA/CCNP students, and anyone working with IP addressing and subnetting. Common use cases include planning office networks, configuring VPCs in AWS/Azure/GCP, setting up VLANs, writing firewall rules, and studying for Cisco certifications.

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Frequently Asked Questions — Subnet Calculator

Free Online Subnet Calculator — IPv4/IPv6 CIDR, VLSM & Network Planning

Subnet Calculator Features

Who Uses a Subnet Calculator?