Subnet Calculator

1. Choose Input Mode: Select "IP + CIDR" to enter a CIDR prefix like /24, or "IP + Subnet Mask" to enter a dotted decimal mask like 255.255.255.0. Both methods produce identical results.
2. Enter the IP address. This can be a host IP or the network address. The calculator will find the correct network address automatically by ANDing the IP with the subnet mask.
3. Enter the prefix length or subnet mask. Common values: /24 (254 hosts), /16 (65,534 hosts), /8 (16.7M hosts). The /30 prefix (2 usable hosts) is popular for point-to-point links.
4. Read the results: Network address (first IP in range), broadcast address (last IP), first and last usable host IPs, the total usable host count, subnet mask in dotted decimal and hex, wildcard mask, and IP class.
5. Use the binary panel to see exactly which bits belong to the network portion and which are host bits. The CIDR table at the bottom shows all common prefixes as a reference.

Subnet Mask   = all 1s for network bits, all 0s for host bits
Wildcard Mask = bitwise NOT of subnet mask (255.255.255.255 - mask)

Network Addr  = IP AND Subnet Mask (bitwise AND)
Broadcast Addr = Network Addr OR Wildcard Mask (bitwise OR)

First Usable Host = Network Addr + 1
Last Usable Host  = Broadcast Addr - 1
Usable Hosts      = 2^(32 - prefix) - 2
Total IPs         = 2^(32 - prefix)

Example: 192.168.1.45/24
  Mask:      255.255.255.0   = 11111111.11111111.11111111.00000000
  Network:   192.168.1.0     (AND of IP and mask)
  Broadcast: 192.168.1.255   (network OR wildcard)
  Wildcard:  0.0.0.255       (bitwise NOT of mask)
  Hosts:     2^8 - 2 = 254

Note: /31 and /32 subnets are special cases. A /31 has 2 IPs and is used for point-to-point links (RFC 3021) with no traditional network/broadcast. A /32 is a host route representing a single IP address.