What this IP address and subnet calculator does
This tool helps you quickly break down an IPv4 address and subnet into the values network engineers use every day: network ID, broadcast address, usable host range, wildcard mask, CIDR prefix, and total host capacity. Instead of doing binary math by hand, you can plug in your values and get an accurate result instantly.
Whether you are studying for a networking certification, planning a VLAN design, troubleshooting routing issues, or checking firewall ACL ranges, a subnet calculator removes guesswork and reduces mistakes.
How to use the calculator
Step-by-step
- Enter an IPv4 address such as 10.20.30.40.
- Enter a subnet as either prefix length (example: 26) or dotted decimal (example: 255.255.255.192).
- Click Calculate.
- Review all derived subnet fields in the output table.
The calculator also handles edge cases like /31 and /32, which are common in point-to-point links and host routes.
IPv4 subnetting refresher
CIDR and subnet masks
CIDR notation (Classless Inter-Domain Routing) expresses the number of network bits in an address. For example, /24 means the first 24 bits identify the network and the remaining 8 bits identify hosts.
- /8 = 255.0.0.0
- /16 = 255.255.0.0
- /24 = 255.255.255.0
- /30 = 255.255.255.252
Network, broadcast, and host range
Every traditional IPv4 subnet includes:
- Network address: first address in the subnet, identifies the subnet itself.
- Broadcast address: last address in the subnet, used to reach all hosts in that subnet.
- Usable host range: addresses between network and broadcast (except special masks such as /31 and /32).
Understanding each calculator result
Key outputs explained
- Subnet mask: dotted decimal form of the CIDR prefix.
- Wildcard mask: inverse of the subnet mask; useful in ACLs and route filters.
- Total addresses: all addresses in the subnet, including network and broadcast (where applicable).
- Usable hosts: count of assignable host IPs in standard host subnets.
- IP scope/type: indicates private, public, loopback, multicast, and related address categories.
Practical subnetting examples
Example 1: Office LAN
If your router interface is 192.168.50.1/24, then the subnet is 192.168.50.0/24 with a broadcast of 192.168.50.255. Usable hosts are 192.168.50.1 through 192.168.50.254, allowing up to 254 devices.
Example 2: Point-to-point link
A WAN link using 203.0.113.8/31 has two addresses and both are usable under RFC 3021: one for each endpoint. This is why /31 behaves differently from traditional host subnet rules.
Common subnetting mistakes to avoid
- Using non-contiguous subnet masks (invalid in modern IP networking).
- Assigning the network or broadcast address to endpoints in standard subnets.
- Confusing wildcard mask with subnet mask in access control lists.
- Forgetting to verify whether an address is private or publicly routable.
Final thoughts
A reliable IP subnet calculator speeds up design and troubleshooting work across routing, switching, cloud networking, and security operations. Use this page whenever you need quick IPv4 subnet math without opening a spreadsheet or doing binary conversion manually.