What is a subnet calculator?

A subnet calculator is a tool that 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.

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.

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. This subnet calculator does this 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 mask is 0.0.0.255. Wildcard masks are used in Cisco ACLs and OSPF configurations.

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.

What is the difference between network address and broadcast address?

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

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.

Is this subnet calculator free?

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's one of 122 free tools at jasperbernaers.com.

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

IP Address

CIDR Prefix

Prefix Length /24

VLSM (Variable Length Subnet Masking) divides a network into subnets of different sizes. Enter a network and add subnets with their required host counts — the planner allocates the most efficient CIDR blocks automatically.

Network Address

CIDR

▸ Subnets Required

Subnet Name

Hosts Needed

Complete IPv4 CIDR cheat sheet — all 33 prefix lengths from /0 to /32 with subnet masks, wildcard masks, total addresses, and usable hosts.

IPv6 Subnet Calculator — enter an IPv6 address with prefix length to see the full network range, total addresses, and expanded notation.

IPv6 Address

Prefix

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. All calculations happen instantly in your browser — no data is sent to a server, no signup required.

Subnet Calculator Features

▸ IPv4 Subnet Calculator — enter any IP address with CIDR prefix (/0 to /32) for instant network address, broadcast, mask, and host range
▸ VLSM Planner — divide a network into variable-length subnets sized to exact host requirements, minimising address waste
▸ CIDR Cheat Sheet — complete reference table of all 33 prefix lengths (/0–/32) with subnet masks, wildcard masks, and usable host counts
▸ IPv6 Calculator — expand compressed IPv6 addresses, calculate network prefix, first/last address, and total address count for any prefix length up to /128
▸ Binary Breakdown — visual binary representation of IP address, subnet mask, and network address, colour-coded by network vs host bits
▸ IP Classification — automatic detection of IP class (A/B/C/D/E), private vs public (RFC 1918), loopback, APIPA, CGNAT, multicast, and reserved ranges

Common Subnet Reference — Most Searched CIDR Blocks

These are the subnets network engineers look up most often. Each row shows the subnet mask, wildcard mask, usable host count, and a typical use case:

CIDR	Subnet Mask	Wildcard	Usable Hosts	Typical Use
/8	255.0.0.0	0.255.255.255	16,777,214	Class A networks (10.0.0.0/8)
/16	255.255.0.0	0.0.255.255	65,534	Large campus / VPC supernets
/24	255.255.255.0	0.0.0.255	254	Standard office / home LAN (192.168.1.0/24)
/25	255.255.255.128	0.0.0.127	126	Split /24 into two equal halves
/26	255.255.255.192	0.0.0.63	62	Small department / VLAN
/27	255.255.255.224	0.0.0.31	30	Server segments / DMZ
/28	255.255.255.240	0.0.0.15	14	Small server cluster / management VLAN
/29	255.255.255.248	0.0.0.7	6	Small server group
/30	255.255.255.252	0.0.0.3	2	Point-to-point WAN links / router interfaces
/32	255.255.255.255	0.0.0.0	1	Host routes, loopback interfaces, firewall rules

RFC 1918 Private Address Ranges

These address blocks are reserved for private networks and are not routed on the public internet. Use them for internal LANs, VPCs, and VLANs:

Range	Class	Total Addresses	Typical Use
10.0.0.0/8	A	16,777,216	Large enterprise networks, cloud VPCs (AWS, Azure, GCP)
172.16.0.0/12	B	1,048,576	Medium-sized networks, Docker default bridge (172.17.0.0/16)
192.168.0.0/16	C	65,536	Home & small office networks (192.168.1.0/24 is the most common LAN)

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 and campus networks with appropriate VLAN segmentation
▸ Configuring VPC subnets in AWS, Azure, or Google Cloud with the right CIDR blocks
▸ Writing Cisco ACLs and OSPF configurations that require wildcard masks
▸ Designing VLSM schemes to maximise IP address efficiency across branch offices
▸ Studying for Cisco CCNA, CCNP, CompTIA Network+, and similar networking certifications
▸ Configuring firewall rules and security groups with precise CIDR-based source/destination filters
▸ Verifying subnetting homework and exam answers with instant binary breakdown

How to Read Subnet Calculator Results

When you enter 192.168.1.100/24, the subnet calculator shows: Network Address 192.168.1.0 (the identifier for the subnet), Broadcast Address 192.168.1.255 (sends to all hosts), Subnet Mask 255.255.255.0 (used in device configuration), Wildcard Mask 0.0.0.255 (used in ACLs and routing protocols), First Usable Host 192.168.1.1, Last Usable Host 192.168.1.254, and 254 usable hosts out of 256 total addresses. The binary breakdown visually separates network bits (first 24) from host bits (last 8), making it clear which portion of the address identifies the network versus the device.

// Subnet Calculator & Network Planner_

Frequently Asked Questions — Subnet Calculator

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

Subnet Calculator Features

Common Subnet Reference — Most Searched CIDR Blocks

RFC 1918 Private Address Ranges

Who Uses a Subnet Calculator?

How to Read Subnet Calculator Results

🌐 Language

// Subnet Calculator & Network Planner_

Frequently Asked Questions — Subnet Calculator

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

Subnet Calculator Features

Common Subnet Reference — Most Searched CIDR Blocks

RFC 1918 Private Address Ranges

Who Uses a Subnet Calculator?

How to Read Subnet Calculator Results