Subnet Calculator
The Subnet Calculator is a utility for calculating IP address ranges, subnet masks, and network parameters based on CIDR notation. It's essential for network planning, IP allocation, and understanding network boundaries.
Opening Subnet Calculator
Access Subnet Calculator in three ways:
- Toolbar Button - Click the Subnet Calculator button in the toolbar
- Menu Bar - Select Tools → Subnet Calculator
- Keyboard Shortcut - Press ⌘T
Calculator Interface
The Subnet Calculator provides an intuitive interface with:
- IP address input field
- CIDR slider (/ 8 to /30)
- Real-time calculation results
- Auto-populated with current interface configuration
Input Fields
IP Address
Enter any IPv4 address within the network you want to calculate.
Format: xxx.xxx.xxx.xxx
Examples: - 192.168.1.1 - 10.0.0.1 - 172.16.50.1
Auto-Populated: When you open the calculator, it automatically fills with your current interface's IP address from the selected interface in Interface Details.
Note: The specific IP you enter doesn't matter—any IP within the subnet will produce the same results for a given CIDR.
CIDR (Classless Inter-Domain Routing)
Use the slider or direct input to select the subnet mask size.
Range: /8 to /30
Format: /XX (where XX is the number of network bits)
Examples: - /24 = 255.255.255.0 (common home/small office network) - /16 = 255.255.0.0 (large corporate network) - /8 = 255.0.0.0 (very large network)
Auto-Populated: Fills with your current interface's CIDR when opened.
Slider Control: Drag slider for easy adjustment, or type directly
IP Range
Format: Start IP - End IP
Example: 192.168.1.1 - 192.168.1.254
Meaning: All usable IP addresses in this subnet (excluding network and broadcast addresses)
Use Case: Determine which IPs are available for assignment
Subnet Mask
Format: Dotted decimal notation
Example: 255.255.255.0
Meaning: The subnet mask corresponding to the selected CIDR
Binary Representation: - 1 bits = network portion - 0 bits = host portion
Common Masks: - /24 = 255.255.255.0 - /16 = 255.255.0.0 - /8 = 255.0.0.0 - /30 = 255.255.255.252 (point-to-point links)
Host Count
Example: 254 hosts
Meaning: Number of usable IP addresses in this subnet
Calculation: 2^(32 - CIDR) - 2
Why -2? Excludes: - Network address (first IP, e.g., 192.168.1.0) - Broadcast address (last IP, e.g., 192.168.1.255)
Examples: - /24 = 254 hosts (2^8 - 2) - /16 = 65,534 hosts (2^16 - 2) - /30 = 2 hosts (2^2 - 2) [common for point-to-point]
Network Address
Example: 192.168.1.0
Meaning: The first IP address in the subnet (not usable for hosts)
Use Case: Identifies the network itself in routing tables
Binary: All host bits set to 0
Broadcast Address
Example: 192.168.1.255
Meaning: The last IP address in the subnet (used for broadcasting to all hosts)
Use Case: Sending packets to all devices in the subnet
Binary: All host bits set to 1
Wildcard Mask
Example: 0.0.0.255
Meaning: Inverse of the subnet mask (used in some routing protocols and ACLs)
Calculation: 255.255.255.255 - Subnet Mask
Use Case: Cisco routers/firewalls, OSPF configurations
Common Wildcards: - /24 → 0.0.0.255 - /16 → 0.0.255.255 - /8 → 0.255.255.255
Binary Subnet Mask
Format: Formatted as 8.8.8.8 (where each octet shows bit count)
Example: 11111111.11111111.11111111.00000000
Meaning: Visual representation of which bits are network (1) vs. host (0)
Use Case: Understanding subnet mask at the binary level
Visual Aid: - Network bits (1s): Left side - Host bits (0s): Right side - Boundary shows where network ends and hosts begin
Common CIDR Sizes
Here's a reference for frequently used subnet sizes:
| CIDR | Subnet Mask | Hosts | Use Case |
|---|---|---|---|
| /30 | 255.255.255.252 | 2 | Point-to-point links (routers) |
| /29 | 255.255.255.248 | 6 | Very small networks |
| /28 | 255.255.255.240 | 14 | Small department |
| /27 | 255.255.255.224 | 30 | Small office |
| /26 | 255.255.255.192 | 62 | Medium office |
| /25 | 255.255.255.128 | 126 | Large office |
| /24 | 255.255.255.0 | 254 | Standard home/small business |
| /23 | 255.255.254.0 | 510 | Large office building |
| /22 | 255.255.252.0 | 1,022 | Small campus |
| /21 | 255.255.248.0 | 2,046 | Medium campus |
| /20 | 255.255.240.0 | 4,094 | Large campus |
| /16 | 255.255.0.0 | 65,534 | Enterprise network |
| /8 | 255.0.0.0 | 16,777,214 | ISP / very large org |
The Subnet Calculator is an essential tool for network planning and troubleshooting. Use it alongside Network Scan to efficiently discover and inventory devices, and verify your network configuration against Interface Details.