Subnet Calculator.
Enter any IPv4 address with CIDR prefix to get subnet mask, network address, broadcast address, host range, and total addresses.
Enter as a.b.c.d/prefix — example: 10.0.0.0/8
Subnet Mask
Network Address
Broadcast Address
First Usable Host
Last Usable Host
Total Addresses
Usable Host Addresses
Binary Representation
Runs entirely in your browser. The values you enter never leave your device — there is no request to our server and nothing is stored. How we handle data
Common Subnet Reference
| CIDR | Subnet Mask | Total Addresses | Usable Hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /30 | 255.255.255.252 | 4 | 2 |
Internal Navigation
IPv4 Subnetting and CIDR Explained Methodology.
The Calculation Branch
Industrial Standards.
All calculations use 32-bit unsigned integer bitwise operations. The IP address and subnet mask are converted to 32-bit integers, bitwise ANDed to find the network address, then the broadcast is found by ORing the network address with the inverse of the mask. All calculations match the IEEE 802 and IETF RFC 1878 definitions.
In-Depth Analysis & Reference Data
Subnetting allows networks to be split into smaller segments for organization, security, and routing efficiency. A single /24 block (256 addresses) can be divided into two /25 blocks (128 each), four /26 blocks (64 each), and so on. Each bit added to the prefix doubles the number of subnets but halves the hosts per subnet. This is used extensively in cloud VPC (Virtual Private Cloud) design, office network segmentation, and data center architecture.
Registry Questions & FAQ.
What are private IP address ranges?
RFC 1918 defines three private IPv4 ranges not routed on the public internet: 10.0.0.0/8 (16M addresses), 172.16.0.0/12 (1M addresses), and 192.168.0.0/16 (65K addresses). Home routers typically use 192.168.1.0/24. Corporate networks often use 10.0.0.0/8 or 172.16.0.0/12. These ranges can be reused by any organization without coordination since they're never exposed publicly.
What is a /30 subnet used for?
A /30 subnet has only 4 addresses: network, 2 hosts, broadcast. It's commonly used for point-to-point links between routers where only 2 IPs are needed (one for each end). Using a /30 wastes only 2 addresses per link instead of 254 (from a wasteful /24), which matters when managing large networks with many router-to-router connections.
Estimates for planning. Always confirm against an authoritative source.