ip and subnet mask calculator

IPv4 Address

Enter a valid IPv4 host address in dotted-decimal format.

Subnet Mask or CIDR Prefix

Supports both subnet mask notation and CIDR notation.

Why an IP and subnet mask calculator matters

Whether you are setting up a home lab, designing enterprise networks, troubleshooting VPN routes, or preparing for networking certifications, subnetting comes up constantly. An IP and subnet mask calculator helps you instantly answer practical questions: What is the network address? Which IPs are usable? What is the broadcast address? How many hosts fit in this subnet?

Doing this manually is still a great skill, but calculators save time and reduce mistakes when you need quick, reliable answers in production environments.

How this calculator works

Enter an IPv4 address and either a subnet mask (like 255.255.255.0) or a CIDR prefix (like /24 or 24). The tool computes:

Network address
Broadcast address
First and last usable host address
Total address count and usable host count
Wildcard mask
Binary representation of the key values

Quick subnetting refresher

IPv4 address structure

An IPv4 address has 32 bits split into four octets (for example, 192.168.1.100). The subnet mask determines which bits represent the network portion and which bits represent the host portion.

Subnet mask vs CIDR notation

The subnet mask 255.255.255.0 is equivalent to /24. CIDR indicates how many leading 1-bits are in the mask. So:

/8 = 255.0.0.0
/16 = 255.255.0.0
/24 = 255.255.255.0
/30 = 255.255.255.252

Common subnet sizes (useful cheat sheet)

/24 → 256 total addresses, 254 traditionally usable hosts
/25 → 128 total addresses, 126 traditionally usable hosts
/26 → 64 total addresses, 62 traditionally usable hosts
/27 → 32 total addresses, 30 traditionally usable hosts
/28 → 16 total addresses, 14 traditionally usable hosts
/29 → 8 total addresses, 6 traditionally usable hosts
/30 → 4 total addresses, 2 traditionally usable hosts

Example

Suppose you enter IP 10.20.30.77 with mask /27. A /27 means blocks of 32 addresses in the last octet. The address 77 falls into the 64–95 block, so:

Network: 10.20.30.64
Broadcast: 10.20.30.95
Usable range: 10.20.30.65 to 10.20.30.94

Common mistakes to avoid

Using an invalid mask that is not contiguous (e.g., 255.0.255.0).
Assigning the network address or broadcast address to hosts (except special cases).
Confusing total addresses with usable host addresses.
Forgetting that /31 and /32 behave differently.

Final thoughts

Good subnetting habits make networks cleaner, safer, and easier to troubleshoot. Use this calculator for fast checks, but keep practicing manual subnet math so you can reason through routing and addressing even without tools.