IPv4 Subnet Calculator
Enter an IP address and CIDR prefix to instantly calculate network details.
Tip: press Enter in either field to calculate.
Why use an online subnet calculator?
Subnetting is one of those skills that seems simple until you need to do it quickly and accurately under pressure. Whether you are a network engineer, student, cloud architect, or IT admin, an online subnet calculator saves time and prevents costly addressing mistakes.
Instead of manually converting binary and decimal values, you can instantly get:
- Network address
- Broadcast address
- Subnet mask and wildcard mask
- Usable host range
- Total and usable hosts per subnet
How subnetting works in plain English
An IPv4 address has 32 bits. The CIDR prefix (for example, /24) tells you how many bits are used for the network portion. The remaining bits are for host addresses inside that subnet.
Quick examples
- /24 → 256 total addresses, 254 usable hosts
- /26 → 64 total addresses, 62 usable hosts
- /30 → 4 total addresses, 2 usable hosts
- /31 → 2 addresses, commonly used for point-to-point links
- /32 → single host route
What this subnet calculator returns
The calculator above provides a complete breakdown for IPv4 subnet planning:
- Input IP (normalized)
- CIDR prefix and subnet mask
- Wildcard mask (useful in ACL design)
- Network address and broadcast address
- First and last usable IP when applicable
- Total and usable address counts
- Binary forms for deeper learning and troubleshooting
When subnet calculators are most helpful
1) VLAN and LAN design
Assign subnets by team, floor, or device type. You can right-size each segment so you avoid both address waste and future expansion issues.
2) Cloud networking
In AWS, Azure, and GCP, subnet planning is critical before deploying workloads. A quick calculator helps you avoid overlapping CIDR ranges across VPCs/VNets and hybrid links.
3) Firewall and ACL configuration
Knowing the network and wildcard values reduces mistakes in access rules and routing policies.
Common subnetting mistakes to avoid
- Using overlapping CIDR ranges between environments
- Forgetting network and broadcast addresses on traditional subnets
- Misreading a dotted mask (255.255.255.192) versus CIDR (/26)
- Allocating too few hosts for growth
- Applying /31 and /32 without understanding their specific use cases
Subnetting cheat-sheet mindset
You do not need to memorize everything. Instead, remember a few anchor points and rely on tools for speed:
- /24 = 256 addresses
- Each +1 in prefix roughly halves host capacity
- Each -1 in prefix roughly doubles host capacity
That simple mental model, plus a reliable calculator, covers most day-to-day planning tasks.
Final thoughts
An online subnet calculator is a practical tool for anyone working with IP addressing. It improves accuracy, reduces deployment errors, and helps you learn subnet math by showing results in both decimal and binary formats. Use it whenever you design new networks, troubleshoot routing issues, or validate security rules.