IPv4 Subnet Calculator
Accurately calculate subnets with our free CIDR subnet calculator. Find subnet masks, IP ranges, and host limits for efficient networking.
Calculating CIDR and determining the correct subnets within a /16 or /19 can be challenging and error-prone when done manually. The process is time-consuming and tedious, with plenty of room for mistakes.
How to Use Our IP Subnet Calculator
- Enter your IPv4 address block in the top-left field of the table.
- Adjust one of the following fields to customize the breakdown (the rest will update automatically); 1. Subnet Mask, 2. Total IPv4 Addresses, 3. Number of Subnets
- Let the calculator do the work—it will generate the correct subnet breakdown based on your input.
- Scroll down to view all results. For a /16 subnet, you’ll see 256 Subnet IDs.
What is an IPv4 Subnet?
An IPv4 subnet is a smaller division of a network, created by applying a subnet mask to split an IP address range into multiple segments. This improves efficiency, security, and performance by reducing broadcast traffic and organizing devices into logical groups. For example, a Class C network (192.168.1.0/24) has a default subnet mask of 255.255.255.0, allowing for 254 usable host addresses. Subnetting can further divide this into smaller networks with fewer hosts.
Subnetting is essential for managing IP allocation, optimizing routing, and securing networks by isolating different areas. CIDR (Classless Inter-Domain Routing) replaces traditional class-based addressing, allowing flexible subnetting with variable-length subnet masks (VLSM). This ensures efficient use of IP addresses in LANs, WANs, and cloud networks.
IPv4 Address Classes
Each class is determined by the first few bits of the IP address and is used for specific purposes.
Class A Subnets
A Class A subnet, or /8, is the 256 Ipv4 blocks in the first octet. Ex. 79.xxx.xxx.0/8
| IPv4 Block Size | Total # of IP’s |
|---|---|
| /8 | 16,777,216 |
| /9 | 8,388,608 |
| /10 | 4,194,304 |
| /11 | 2,097,152 |
| /12 | 1,048,576 |
| /13 | 524,288 |
| /14 | 262,144 |
| /15 | 131,072 |
Class B Subnets
A Class B subnet, or /16, is the 256 blocks in the second octet. Ex. xxx.79.xxx.0/16
| IPv4 Block Size | Total # of IP’s |
|---|---|
| /16 | 65,536 |
| /17 | 32,768 |
| /18 | 16,384 |
| /19 | 8,192 |
| /20 | 4,096 |
| /21 | 2,046 |
| /22 | 1,022 |
| /23 | 510 |
Class C Subnets
A Class C subnet, a /24, is the 256 blocks in the third octet. Ex. xxx.xxx.79.0/16
| IPv4 Block Size | Total # of IP’s |
|---|---|
| /24 | 256 |
| /25 | 128 |
| /26 | 64 |
| /27 | 32 |
| /28 | 16 |
| /29 | 8 |
| /30 | 4 |
| /31 | 2 |
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