Subnet Calculator | TheSmartCalculator - Free Online Calculators

IP Address

Subnet Mask (CIDR)

About the Subnet Calculator

Subnetting is a fundamental skill for network engineers, system administrators, and IT professionals. Dividing an IP address space into subnets improves network performance, security, and manageability. Our Subnet Calculator performs all the standard subnetting calculations instantly — no pencil and paper, no memorizing formulas.

Enter any IPv4 address and subnet mask (or CIDR notation), and get the network address, broadcast address, usable host range, wildcard mask, total hosts, and usable hosts in seconds.

How It Works

Enter an IPv4 address and either a subnet mask (e.g., 255.255.255.0) or CIDR prefix (e.g., /24). The calculator converts to binary, performs bitwise AND operations to find the network address, computes the broadcast address, and derives all related subnet information.

Formula / Key Reference

Network Address = IP AND Subnet Mask (bitwise)

Broadcast Address = Network Address OR (NOT Subnet Mask)

First Usable Host = Network Address + 1

Last Usable Host = Broadcast Address − 1

Total Hosts = 2^(32 − prefix length)

Usable Hosts = Total Hosts − 2 (network and broadcast addresses)

Real-World Example

IP Address: 192.168.10.50

Subnet Mask: 255.255.255.0 (/24)

Network Address: 192.168.10.0

Broadcast Address: 192.168.10.255

First Usable Host: 192.168.10.1

Last Usable Host: 192.168.10.254

Total Hosts: 2^8 = 256

Usable Hosts: 254

Wildcard Mask: 0.0.0.255

Now if you subnet further to /26 (255.255.255.192):

Total hosts per subnet: 2^6 = 64 (62 usable)

Number of /26 subnets in this /24: 4

Subnet ranges:

192.168.10.0 – 192.168.10.63

192.168.10.64 – 192.168.10.127

192.168.10.128 – 192.168.10.191

192.168.10.192 – 192.168.10.255

Common Uses

Network planning and segmentation for enterprise environments

Configuring routers, firewalls, and switches with correct subnet parameters

IT certifications: CompTIA Network+, CCNA, and other networking exams

Troubleshooting IP addressing conflicts and routing issues

Cloud networking: AWS VPC, Azure Virtual Network subnet planning

Frequently Asked Questions

What is CIDR notation? ▼

CIDR (Classless Inter-Domain Routing) notation expresses a subnet mask as a prefix length — the number of consecutive 1-bits in the mask. /24 means 24 bits are the network portion (equivalent to 255.255.255.0). /16 means 16 bits (255.255.0.0). CIDR replaced the old Class A/B/C system for more flexible IP allocation.

Why are there always 2 fewer usable hosts than total hosts? ▼

The first address in every subnet (all host bits = 0) is reserved as the network address, used to identify the subnet itself. The last address (all host bits = 1) is the broadcast address, used to send packets to all hosts in the subnet simultaneously. These two addresses cannot be assigned to individual hosts.

What is the difference between public and private IP addresses? ▼

Private IP addresses (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are used within local networks and are not routable on the public internet. Public IPs are globally unique and assigned by ISPs. NAT (Network Address Translation) allows many devices with private IPs to share a single public IP address.

How do I choose the right subnet size? ▼

Calculate the maximum number of hosts you'll need in the subnet, then choose the smallest subnet that accommodates them with some room for growth. For 50 hosts, a /26 (62 usable hosts) is sufficient. For 200 hosts, a /24 (254 usable hosts) works. Smaller subnets improve security by limiting broadcast domains.