IPv4 Subnet Calculator
Use this free online subnet mask calculator to find the network address, broadcast address, host range, wildcard mask, and usable hosts.
What is an online IP subnet calculator?
An online IP subnet calculator is a networking tool that helps you break an IPv4 network into logical segments. Instead of manually calculating subnet masks and host ranges, you can enter an IP address and CIDR prefix (like /24 or /27) and get immediate results.
This is useful for system administrators, DevOps engineers, students, help desk teams, and anyone configuring routers, firewalls, VLANs, VPN tunnels, or cloud networks.
How to use this CIDR calculator
- Enter a valid IPv4 address (for example,
192.168.1.130). - Enter the prefix length from
0to32. - Click Calculate Subnet.
- Review the full output including subnet mask, network ID, broadcast, and host capacity.
What the results mean
Network Address
The first address in the subnet. It identifies the subnet itself and cannot be assigned to a regular host.
Broadcast Address
The last address in the subnet. Traffic sent to this address is delivered to all hosts in that subnet (except in /31 and /32 special cases).
Usable Host Range
The assignable host IP range between network and broadcast addresses. For typical subnets, this excludes the first and last address.
Subnet Mask and Wildcard Mask
The subnet mask (like 255.255.255.0) determines network vs host bits. The wildcard mask is its inverse and is often used in ACL rules.
Total and Usable Hosts
Total addresses are based on the number of host bits. Usable hosts are generally total minus two, with edge-case behavior for /31 and /32.
Common IPv4 subnet sizes
- /24 → 256 total addresses, 254 usable
- /25 → 128 total addresses, 126 usable
- /26 → 64 total addresses, 62 usable
- /27 → 32 total addresses, 30 usable
- /28 → 16 total addresses, 14 usable
- /29 → 8 total addresses, 6 usable
- /30 → 4 total addresses, 2 usable (common for point-to-point)
Why subnet planning matters
Good subnet design improves security, reduces broadcast traffic, and makes troubleshooting easier. It also prevents address waste by sizing each subnet based on actual demand. In cloud environments and hybrid networks, clean subnet boundaries simplify routing and access control.
Quick best practices
- Leave growth space when choosing subnet size.
- Document VLAN IDs, subnets, and gateway addresses together.
- Reserve small dedicated subnets for infrastructure and management.
- Validate overlap before deploying VPNs or peering connections.
- Use a reliable subnet mask calculator when planning changes.
Bookmark this page whenever you need a fast, accurate IPv4 subnet calculator for network design, exam prep, or day-to-day operations.