About Subnet Calculator
Subnet Calculator is a free online tool that computes subnet details from CIDR notation (e.g., 192.168.1.0/24) or an IP address with a subnet mask. It calculates the network address, broadcast address, usable host range, total hosts, wildcard mask, and more using pure bitwise operations.
How to Use
- Enter CIDR — Type a CIDR notation like 192.168.1.0/24 in the input field.
- Or use IP + Mask — Enter an IP address and subnet mask separately.
- Use presets — Click common CIDR presets (/8, /16, /24, /28, /30, /32) for quick calculations.
- View results — See network address, broadcast, host range, total hosts, and more.
Frequently Asked Questions
Q: What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length (e.g., /24). The prefix indicates how many bits are used for the network portion.
Q: What is a subnet mask?
A subnet mask defines which portion of an IP address is the network and which is the host. For example, 255.255.255.0 (/24) means the first 24 bits are network and the last 8 bits are host.
Q: What is a wildcard mask?
A wildcard mask is the inverse of the subnet mask. It's commonly used in ACLs (Access Control Lists) on routers. For a /24 subnet, the wildcard mask is 0.0.0.255.
Q: Why are 2 addresses subtracted from total hosts?
The network address (first) and broadcast address (last) cannot be assigned to hosts, so usable hosts = 2^(32 - prefix) - 2.
Q: What is the smallest usable subnet?
A /30 subnet is the smallest usable subnet, providing 2 usable host addresses (one for each end of a point-to-point link). A /31 can be used for point-to-point links per RFC 3021, and /32 represents a single host address.