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IP Subnet Calculator

Calculate IP subnets, network addresses, broadcast addresses, and available hosts from CIDR notation.

An IP subnet calculator computes network addresses, broadcast addresses, host ranges, and CIDR notation for IPv4 subnetting.

Enter an IPv4 address and the CIDR prefix length (e.g. 24 for a /24 subnet). The calculator will determine the network address, broadcast address, usable host range, and subnet mask.

Examples

192.168.1.100 /24

Subnet mask: 255.255.255.0, Network: 192.168.1.0, Broadcast: 192.168.1.255, Usable range: 192.168.1.1 - 192.168.1.254 (254 hosts).

10.0.0.50 /16

Subnet mask: 255.255.0.0, Network: 10.0.0.0, Broadcast: 10.0.255.255, Usable hosts: 65,534.

Frequently Asked Questions

What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation uses a slash followed by a number (e.g. /24) to indicate how many bits of the IP address are used for the network portion. A /24 means the first 24 bits identify the network, leaving 8 bits for host addresses.
What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. Where the subnet mask has 1s, the wildcard has 0s and vice versa. It is commonly used in access control lists (ACLs) on network devices.
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Quick Tips

  • •Use /24 (255.255.255.0) for most small office and home networks — it provides 254 usable hosts.
  • •For point-to-point links between two routers, a /30 subnet wastes only 2 addresses.
  • •Always document your subnet assignments in a spreadsheet or IPAM tool to avoid overlapping ranges.

An IP subnet calculator computes network addresses, broadcast addresses, host ranges, and CIDR notation for IPv4 subnetting.

How to Use This Calculator

Enter an IPv4 address and the CIDR prefix length (e.g. 24 for a /24 subnet). The calculator will determine the network address, broadcast address, usable host range, and subnet mask.

Understanding the Formula

Subnet Mask = 2^32 shifted left by (32 - CIDR). Network Address = IP AND Subnet Mask. Broadcast = Network OR Wildcard Mask. Usable Hosts = 2^(32 - CIDR) - 2.

Examples

192.168.1.100 /24

Subnet mask: 255.255.255.0, Network: 192.168.1.0, Broadcast: 192.168.1.255, Usable range: 192.168.1.1 - 192.168.1.254 (254 hosts).

10.0.0.50 /16

Subnet mask: 255.255.0.0, Network: 10.0.0.0, Broadcast: 10.0.255.255, Usable hosts: 65,534.

Frequently Asked Questions

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation uses a slash followed by a number (e.g. /24) to indicate how many bits of the IP address are used for the network portion. A /24 means the first 24 bits identify the network, leaving 8 bits for host addresses.

What is a wildcard mask?

A wildcard mask is the inverse of the subnet mask. Where the subnet mask has 1s, the wildcard has 0s and vice versa. It is commonly used in access control lists (ACLs) on network devices.

Assumptions & Limitations

  • IPv4 only; IPv6 subnetting uses a different notation and much larger address space.
  • Usable host count subtracts 2 from the total addresses (network and broadcast) for prefix lengths shorter than /31.
  • Private vs. public classification follows RFC 1918 ranges and does not detect carrier-grade NAT (100.64.0.0/10).