Tip: You can enter 24, /24, or 255.255.255.0.
What is an IP address calculator online?
An IP address calculator online is a quick networking tool that helps you convert an IP + subnet into useful details such as network address, broadcast address, host range, wildcard mask, and host capacity. It is often called a subnet calculator, CIDR calculator, or IPv4 network calculator.
Whether you are configuring a home router, planning VLANs in an office, preparing for a networking exam, or troubleshooting address conflicts, this tool removes manual binary math and gives instant, reliable results.
How to use this calculator
Step 1: Enter an IPv4 address
Use dotted decimal format such as 10.0.15.7 or 172.16.4.12.
Each octet must be between 0 and 255.
Step 2: Enter subnet information
You can type a CIDR prefix (for example 26 or /26) or a subnet mask
(255.255.255.192). The calculator validates the mask and converts it to CIDR automatically.
Step 3: Review the output
- Network Address: the start of the subnet block.
- Broadcast Address: the final address in the subnet block.
- First / Last Host: usable host range (with /31 and /32 special behavior).
- Total / Usable Addresses: capacity planning values.
- Class and Type: quick context (A/B/C, private/public, loopback, etc.).
Why this matters for real networks
Correct subnetting is essential for clean routing, security boundaries, and predictable capacity. A wrong prefix can isolate hosts, create overlapping ranges, or waste large blocks of addresses. Using an online IP subnet calculator reduces these mistakes and speeds up deployment.
Common use cases
- Designing LAN segments and VLANs
- Splitting a large network into smaller subnets
- Troubleshooting “host unreachable” errors
- Validating firewall object ranges
- Studying for CCNA, Network+, and cloud networking exams
CIDR quick reference (IPv4)
- /24 → 256 total, 254 usable (classic small LAN)
- /25 → 128 total, 126 usable
- /26 → 64 total, 62 usable
- /27 → 32 total, 30 usable
- /28 → 16 total, 14 usable
- /29 → 8 total, 6 usable
- /30 → 4 total, 2 usable (point-to-point style)
- /31 → 2 total, 2 usable in modern point-to-point links
- /32 → single host route
Frequently asked questions
Is this calculator for IPv4 or IPv6?
This page focuses on IPv4 subnet calculations. IPv6 uses different addressing rules and notation.
Can I enter a subnet mask instead of CIDR?
Yes. Enter values like 255.255.255.0, 255.255.254.0, or
255.255.255.248. The mask must be valid and contiguous.
What happens with /31 and /32?
For /31, both addresses can be usable on point-to-point links.
For /32, the subnet represents a single host address.
Final thoughts
A reliable IP address calculator online is one of the most practical tools for network engineers, system admins, students, and IT support teams. Use it to verify subnet math quickly, prevent addressing mistakes, and build cleaner, more maintainable networks.