subnet calculator
Subnet Calculator
Enter any IPv4 address and CIDR prefix to instantly calculate network address, broadcast, usable host range, subnet mask, and binary breakdown.
| IP Address | — |
| Network Address | — |
| Broadcast | — |
| Subnet Mask | — |
| Wildcard Mask | — |
| First Host | — |
| Last Host | — |
| IP Class | — |
| Address Type | — |
| Host Bits | — |
The bar above shows how this subnet sits within its parent address space. Orange = your network block · Blue = remaining space in this class.
🔒 VLSM Planner — Pro feature
Split this network into multiple subnets of different sizes. Supports unlimited subnets, export to CSV, and saves to your history. Available in NetITPro Pro.
Subnetting — frequently asked questions
What is a subnet calculator?
A subnet calculator takes an IPv4 address and a CIDR prefix length (e.g. /24) and automatically computes the network address, broadcast address, subnet mask, wildcard mask, first and last usable host IP, and the total number of usable host addresses in that subnet — saving you from doing the binary math by hand.
How do I calculate a subnet mask from a CIDR prefix?
Write 32 bits with the first N bits set to 1 and the remaining bits set to 0, where N is the prefix length. For example, /24 gives 11111111.11111111.11111111.00000000, which converts to 255.255.255.0. Each group of 8 bits maps to one octet of the dotted-decimal mask.
How many usable hosts are in a /24 subnet?
A /24 subnet has 256 total IP addresses (2⁸). Two are reserved — the network address (.0) and the broadcast address (.255) — leaving 254 usable host addresses in the range .1 through .254. The formula for usable hosts is 2^(32−prefix) − 2.
What is the difference between a network address and a broadcast address?
The network address is the first address in a subnet (all host bits = 0) and identifies the subnet itself — it cannot be assigned to a host. The broadcast address is the last address (all host bits = 1) and sends packets to every host in the subnet simultaneously. Neither can be used as a host IP address.
What is a wildcard mask and where is it used?
A wildcard mask is the bitwise inverse of the subnet mask — calculated by subtracting each octet from 255. A mask of 255.255.255.0 gives wildcard 0.0.0.255. Wildcard masks are used in Cisco IOS access control lists (ACLs) and OSPF network statements to specify which bits of an address must match a given pattern.
What are RFC 1918 private IP address ranges?
RFC 1918 defines three private IPv4 ranges that are not routed on the public internet:
10.0.0.0/8— Class A, ~16.7 million addresses172.16.0.0/12— Class B, ~1 million addresses192.168.0.0/16— Class C, 65,536 addresses
These are used for internal LANs and require NAT to reach the public internet.
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation represents an IP address combined with its network prefix length as a single string separated by a slash — e.g. 192.168.1.0/24. The number after the slash indicates how many bits identify the network. CIDR replaced the older classful A/B/C system to allow more flexible, efficient IP address allocation and route summarisation.
How do I find the network address of a subnet?
Perform a bitwise AND between the IP address and the subnet mask. Example: IP 192.168.1.100, mask 255.255.255.0:
192 AND 255 = 192 · 168 AND 255 = 168 · 1 AND 255 = 1 · 100 AND 0 = 0
Network address = 192.168.1.0. This calculator does the AND operation automatically.