An IP subnet calculator helps network engineers and system administrators quickly determine network boundaries, usable host ranges, and subnet details from CIDR notation. Enter any IPv4 address with a prefix length or subnet mask to instantly see all relevant network information for planning, troubleshooting, or documentation.
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IPv4 Subnet Cheat Sheet
| CIDR | Subnet Mask | Wildcard | Total Addresses | Usable Hosts |
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How to Use the IP Subnet Calculator
Subnetting is a fundamental networking skill, but doing the math by hand is tedious and error-prone. This IP subnet calculator lets you instantly compute all the details you need — network address, broadcast, host range, wildcard mask — from any IPv4 address and CIDR prefix length or subnet mask.
Step 1: Enter an IP Address
Type any valid IPv4 address into the IP Address field. This can be a network address like 192.168.1.0, a host address like 10.0.5.42, or any address within the subnet you want to analyze. The calculator determines the correct network boundaries automatically.
Step 2: Set the Prefix Length or Subnet Mask
Choose a CIDR prefix from the dropdown (ranging from /8 to /30) or type a subnet mask in dotted decimal notation like 255.255.255.0. The two inputs stay synchronized — changing one automatically updates the other. Common choices include /24 for small LANs (254 hosts), /16 for medium networks, and /30 for point-to-point links.
Step 3: Review the Results
After clicking Calculate, you'll see the network address, broadcast address, first and last usable hosts, total host count, IP class (A/B/C), and whether the address is in a private RFC 1918 range. The binary representation of the subnet mask helps you visualize exactly which bits belong to the network versus host portion.
Step 4: Use the Cheat Sheet
Expand the subnet cheat sheet at the bottom for a quick-reference table of all prefix lengths from /8 to /30, complete with subnet masks, wildcard masks, and host counts. This is especially handy when planning network segmentation or studying for the CCNA exam.
Common Subnetting Scenarios
Use /24 for a standard office or home LAN with up to 254 devices. Use /28 to carve a larger network into 14-host segments — ideal for VLANs or DMZs. Use /30 for router-to-router point-to-point links that only need two addresses. All calculations run locally in your browser, making it safe to use with production network data.
Frequently Asked Questions
Is this IP subnet calculator completely free?
Yes, this IP subnet calculator is 100% free with no limits. You can calculate as many subnets as you need without creating an account. There are no usage caps, no premium tier, and no ads blocking the results.
Is my data safe when using this tool?
Absolutely. All calculations run entirely in your browser using client-side JavaScript. Your IP addresses and network information are never sent to any server, never stored, and never logged. It is completely safe to use with production network data.
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation is a compact way to specify an IP address and its associated subnet mask. It uses a slash followed by a number (e.g., /24) that indicates how many bits of the address are used for the network portion. For example, 192.168.1.0/24 means the first 24 bits identify the network.
How do I convert a subnet mask to CIDR notation?
Count the number of consecutive 1-bits in the subnet mask's binary representation. For example, 255.255.255.0 is 11111111.11111111.11111111.00000000, which has 24 ones, so it equals /24. This tool lets you enter either format and automatically converts between them.
What is the difference between network address and broadcast address?
The network address is the first address in a subnet and identifies the network itself — it cannot be assigned to a host. The broadcast address is the last address and is used to send data to all hosts in the subnet. Neither can be used as a host address, which is why usable hosts equals total addresses minus two.
What are RFC 1918 private IP addresses?
RFC 1918 defines three private IP address ranges reserved for internal networks: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These addresses are not routable on the public internet and are commonly used for home and corporate LANs. This tool automatically detects whether your IP falls within these ranges.
What is a wildcard mask and when do I need it?
A wildcard mask is the inverse of a subnet mask — where the subnet mask has a 1, the wildcard mask has a 0, and vice versa. It is primarily used in Cisco router ACLs (access control lists) and OSPF configurations. For example, a /24 subnet mask of 255.255.255.0 has a wildcard mask of 0.0.0.255.