Subnet Calculator

What is Subnet Calculator?

Subnet Calculator performs IPv4 and IPv6 subnet calculations including network address, broadcast address, usable host range, wildcard mask, and the number of available hosts for any CIDR notation or subnet mask. It supports subnet splitting (dividing a network into smaller subnets), supernetting (aggregating contiguous subnets), and VLSM (Variable Length Subnet Masking) planning for efficient address allocation. The tool visualizes subnet hierarchies and checks for overlapping address ranges.

Network engineers designing IP address schemes, cloud architects configuring VPC subnets, and sysadmins troubleshooting network connectivity. The tool runs entirely in your browser — your data never leaves your device.

How to Use Subnet Calculator

1. Enter an IP address with CIDR notation (192.168.1.0/24) or with a subnet mask
2. View the calculated network address, broadcast address, host range, and available hosts
3. Use the subnet splitter to divide the network into equal or variable-sized subnets
4. Check subnet overlap by entering multiple CIDR blocks for comparison

Common Use Cases

• Planning IP address allocation for a new office network with multiple VLANs
• Calculating the usable host range for a given CIDR block in AWS VPC configuration
• Determining the optimal subnet mask to accommodate a specific number of hosts
• Checking whether two subnets overlap before configuring routing tables or firewall rules

Pro Tips

• A /24 subnet has 256 addresses but only 254 usable hosts — the first address is the network address and the last is the broadcast address; AWS reserves 5 addresses per subnet (network, broadcast, +1 for router, +2 for DNS, +3 for future use)
• Use VLSM instead of equal subnetting — allocating a /28 (14 hosts) for a 10-device subnet and a /25 (126 hosts) for a 100-device subnet wastes fewer addresses than giving both a /24
• For quick mental math: each additional CIDR bit halves the address count — /24 = 256, /25 = 128, /26 = 64, /27 = 32, /28 = 16; this pattern makes it easy to estimate subnet sizes without a calculator

Why Use This Tool?

• Privacy-first: All processing happens locally in your browser. No data is transmitted to any server.
• No installation required: Works in any modern browser on desktop or mobile.
• Completely free: No account, no credit card, no usage caps.
• Fast and reliable: Powered by modern Web APIs for near-instant results.

Related Concepts

Learn more about related topics: CIDR notation, VLSM, Network address, Broadcast address.

Frequently Asked Questions