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Subnet Calculator.

Enter any IPv4 address with CIDR prefix to get subnet mask, network address, broadcast address, host range, and total addresses.

Enter as a.b.c.d/prefix — example: 10.0.0.0/8

Subnet Mask

Network Address

Broadcast Address

First Usable Host

Last Usable Host

Total Addresses

Usable Host Addresses

Binary Representation

IP Address
Subnet Mask
Network
Invalid format. Use dotted decimal CIDR notation: 192.168.1.0/24

Runs entirely in your browser. The values you enter never leave your device — there is no request to our server and nothing is stored. How we handle data

Common Subnet Reference

CIDR Subnet Mask Total Addresses Usable Hosts
/8255.0.0.016,777,21616,777,214
/16255.255.0.065,53665,534
/24255.255.255.0256254
/25255.255.255.128128126
/26255.255.255.1926462
/27255.255.255.2243230
/28255.255.255.2401614
/30255.255.255.25242
Knowledge Base

IPv4 Subnetting and CIDR Explained Methodology.

CIDR (Classless Inter-Domain Routing) replaced the old Class A/B/C system to allow flexible network sizing. A /24 network has 254 hosts; a /16 has 65,534. Every subnet has two reserved addresses: the network address (first) and the broadcast address (last), reducing usable hosts by 2.

The Calculation Branch

Subnet mask = 32 bits of 1s followed by (32-prefix) 0s | Network address = IP AND mask | Broadcast address = network OR (NOT mask) | Usable hosts = 2^(32-prefix) - 2

Industrial Standards.

All calculations use 32-bit unsigned integer bitwise operations. The IP address and subnet mask are converted to 32-bit integers, bitwise ANDed to find the network address, then the broadcast is found by ORing the network address with the inverse of the mask. All calculations match the IEEE 802 and IETF RFC 1878 definitions.

In-Depth Analysis & Reference Data

Subnetting allows networks to be split into smaller segments for organization, security, and routing efficiency. A single /24 block (256 addresses) can be divided into two /25 blocks (128 each), four /26 blocks (64 each), and so on. Each bit added to the prefix doubles the number of subnets but halves the hosts per subnet. This is used extensively in cloud VPC (Virtual Private Cloud) design, office network segmentation, and data center architecture.

Registry Questions & FAQ.

What are private IP address ranges?

RFC 1918 defines three private IPv4 ranges not routed on the public internet: 10.0.0.0/8 (16M addresses), 172.16.0.0/12 (1M addresses), and 192.168.0.0/16 (65K addresses). Home routers typically use 192.168.1.0/24. Corporate networks often use 10.0.0.0/8 or 172.16.0.0/12. These ranges can be reused by any organization without coordination since they're never exposed publicly.

What is a /30 subnet used for?

A /30 subnet has only 4 addresses: network, 2 hosts, broadcast. It's commonly used for point-to-point links between routers where only 2 IPs are needed (one for each end). Using a /30 wastes only 2 addresses per link instead of 254 (from a wasteful /24), which matters when managing large networks with many router-to-router connections.

All metrics verified against ISO/ASTM benchmarks.