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IP Subnet Calculator - Netmask & CIDR Calculator

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.

IP Address & CIDR

Examples:

Subnet Information

Options

How It Works

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Enter Network Details

Paste CIDR blocks (e.g., 10.0.0.0/16) or individual addresses. The calculator validates IPv4 syntax and highlights formatting mistakes before processing.

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Select Calculation Mode

Switch between calculations, validations, or subnet splitting. Toggle broadcast, wildcard, binary views, and choose detailed, compact, or tabular output formats.

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Review Rich Network Data

Receive instant results with network/broadcast addresses, usable host ranges, classification, private/multicast flags, and optional binary breakdown for ACL work.

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Export & Document

Copy the generated markdown-style report, download output, or store runs in tool history to share with teammates and paste into change requests.

Problems It Solves

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Problem

Subnet math by hand is slow and error-prone, especially when juggling multiple VLANs or address pools under deadline.

Solution

Compute masks, usable ranges, totals, and binary representations instantly so network engineers can focus on architecture instead of arithmetic.

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Problem

Documentation requires consistent reporting of private status, network class, and wildcard masks for security reviews.

Solution

Auto-generated summaries include private/public flags, loopback/multicast indicators, and wildcard masks ready for ACLs and change tickets.

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Problem

Splitting address space into even subnets can be confusing without visualizing the new ranges and host counts.

Solution

Use the split mode to carve networks into equal subnets with clear start/end addresses and host availability for each child subnet.

Why Choose This Tool

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Private & Offline

Network inventories, infrastructure plans, and customer ranges stay on your device. Ideal for sensitive enterprise environments.

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Operator-Grade Detail

Fields for wildcard masks, binary output, and classification mirror what engineers need for ACLs, BGP policies, and firewall rules.

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Flexible Output

Switch between detailed markdown, compact summaries, or tables to match internal documentation standards and runbooks.

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Integrated History

Revisit previous calculations through tool history, making audits and troubleshooting faster when networks evolve.

Frequently Asked Questions

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.

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