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IP Subnet Calculator – Calculate CIDR & Subnet Masks

Calculate subnet masks, CIDR ranges, usable IPs, and network details with visual subnet splitting and VLSM support.

🟢 Runs locally · no uploads

IP Subnet Calculator

Calculate subnet masks and IP ranges

lightbulbPopular Use Cases

home
Home Network Setup

Calculate subnet mask for typical home network (192.168.1.0/24)

business
Office Network Planning

Design office network subnets for multiple departments and VLANs

cloud
Cloud VPC Configuration

Calculate subnets for AWS VPC or Azure VNet deployments

lan
Network Segmentation

Plan VLAN subnets for security zones and network isolation

numbers Network Input
192.168.1.0/24
table_rows Calculation Results
table_rows
Calculation results will appear here
Keyboard Shortcuts: Ctrl+V to paste • Ctrl+Enter to calculate

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› About this tool · FAQ

Calculate IP subnets, netmasks, CIDR notation, and find first/last usable IP addresses. Complete network calculator with subnet splitting and binary analysis for network engineers.

How do I find the first usable IP address in a subnet?

The first usable IP address is always the network address + 1. For example, in subnet 192.168.1.0/24, the network address is 192.168.1.0, so the first usable IP is 192.168.1.1. This calculator shows you both automatically.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation represents an IP network using an IP address followed by a slash and the number of network bits (e.g., 192.168.1.0/24). The number after the slash indicates how many bits are used for the network portion.

How do I calculate the number of usable hosts?

The number of usable hosts equals 2^(32-CIDR) - 2. The -2 accounts for the network address (first IP) and broadcast address (last IP) which cannot be assigned to hosts.

What are private IP address ranges?

Private IP ranges are: 10.0.0.0/8 (Class A), 172.16.0.0/12 (Class B), and 192.168.0.0/16 (Class C). These addresses are not routed on the public internet and are used for internal networks.

What is a wildcard mask?

A wildcard mask is the inverse of a subnet mask. It shows which bits are ignored when matching IP addresses. It's commonly used in access control lists (ACLs) and routing protocols.

How does subnet splitting work?

Subnet splitting divides a larger network into smaller subnets by borrowing bits from the host portion. Each split requires additional network bits, reducing the number of available host addresses per subnet.