Subnet Calculator and CIDR Cheat Sheet for iOS

Subnetting Made Simple

Subnetting is one of those networking fundamentals that everyone needs to know but nobody wants to calculate by hand. Whether you're setting up VLANs, configuring firewall rules, or planning IP address allocation, a subnet calculator saves time and prevents mistakes.

NetKit Pro's IP Tools puts a full subnet calculator on your iPhone — no more Googling conversion tables.

What IP Tools Includes

The IP Tools suite in NetKit Pro covers:

• Subnet Calculator: Enter an IP and CIDR prefix to get network address, broadcast, host range, and host count
• CIDR Converter: Convert between CIDR notation and dotted-decimal subnet masks
• IP Geolocation: Look up the approximate geographic location of any public IP

How to Use the Subnet Calculator

1. Open NetKit Pro and navigate to IP Tools
2. Enter an IP address (e.g., 192.168.1.100)
3. Select the CIDR prefix length (e.g., /24)
4. View the calculated results:
5. Network Address: 192.168.1.0
6. Broadcast Address: 192.168.1.255
7. First Host: 192.168.1.1
8. Last Host: 192.168.1.254
9. Total Hosts: 254
10. Subnet Mask: 255.255.255.0

CIDR Reference Table

Bookmark this post for quick reference. Here are the most commonly used CIDR prefixes:

Private IP Ranges

These are the IP ranges reserved for private use (RFC 1918). You'll encounter them in virtually every local network:

Quick Mental Math for Subnetting

Here's a trick for quickly calculating subnets without a calculator:

For /24 and above (common subnets):

1. Start with 256
2. Subtract the last octet of the subnet mask
3. That's your block size

Example: What are the subnets for /26 (255.255.255.192)?

• Block size: 256 - 192 = 64
• Subnets: .0, .64, .128, .192
• Each has 62 usable hosts

For quick host counts:

The formula is: 2^(32 - prefix) - 2

• /24: 2^8 - 2 = 254 hosts
• /25: 2^7 - 2 = 126 hosts
• /26: 2^6 - 2 = 62 hosts
• /27: 2^5 - 2 = 30 hosts

When to Subnet

Common scenarios where subnetting comes up:

• VLANs: Segmenting a network for security or performance
• Cloud infrastructure: Sizing VPC subnets in AWS, Azure, or GCP
• Home lab: Setting up multiple networks on a single router
• Firewall rules: Defining allow/deny rules by subnet
• IP planning: Allocating address space across offices or departments

Get NetKit Pro

IP Tools is included in NetKit Pro alongside 11 other network tools. Available on the App Store as a one-time purchase — no subscriptions, no ads.