Subnet Calculator

Calculate network, broadcast, host range, and mask details from CIDR
This free online subnet calculator runs in your browser and is part of our Calculators collection.

Subnet Calculator

Calculate network details from an IPv4 address and CIDR prefix.

Included values

  • Network, broadcast, first and last usable addresses
  • Subnet mask and wildcard mask
  • Total and usable host counts
  • Binary mask breakdown for study and debugging
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Instant In-Browser Execution Runs locally in JavaScript without wait times or server delays.
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100% Privacy & Security Your inputs and files are never stored or logged on remote servers.
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Cross-Device Responsive Fully optimized for mobile smartphones, tablets, and desktop displays.
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100% Free Forever No subscription fees, no signups, and no software installations.

How to Use the Online Subnet Calculator

1 Enter IP Address & CIDR Prefix

Input an IP address and select the CIDR subnet mask prefix from /1 to /32 (e.g. `192.168.1.0/24`).

2 Inspect Network & Broadcast Boundaries

View the calculated Network Address, Broadcast Address, Subnet Mask, and Wildcard Mask.

3 Review Usable Host Range

Inspect the First Usable Host IP, Last Usable Host IP, and Total Usable Hosts capacity.

4 Examine Binary Subnet Breakdown

Inspect the 32-bit binary bitwise AND visualization showing the network prefix bits versus host identifier bits.

Frequently Asked Questions

Common questions about using this free online subnet calculator.

What does the CIDR prefix slash notation (e.g. `/24`) mean? ▾
CIDR (Classless Inter-Domain Routing) prefix notation indicates how many leading bits out of 32 belong to the network prefix. For example, `/24` means the first 24 bits are 1s (`255.255.255.0`), leaving 8 bits for host addresses (2^8 = 256 addresses).
Why are the total usable hosts 2 less than the total IP addresses? ▾
In standard IPv4 subnets, the very first address in the block is reserved as the Network Identifier, and the very last address is reserved as the Subnet Broadcast Address. Therefore, Usable Hosts = `2^(32 − CIDR) − 2`.
What is a Wildcard Mask used for in networking? ▾
A wildcard mask is the exact inverted complement of a subnet mask (where 0s represent network bits and 1s represent host bits). It is used in Cisco IOS Access Control Lists (ACLs) and OSPF routing protocols.
What are /30, /31, and /32 subnets used for? ▾
A `/30` provides 2 usable hosts, traditionally used for point-to-point router links. A `/31` (RFC 3021) provides 2 usable hosts with no broadcast on modern point-to-point links. A `/32` represents a single host loopback address.

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