What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated routing prefix using a slash followed by the number of leading 1-bits in the subnet mask (e.g. 192.168.1.0/24 means the first 24 bits belong to the network prefix).

Why are there 2 fewer usable hosts than total IP addresses in a subnet?

In standard IPv4 subnets (prefix /30 and lower), the very first address in the block is reserved as the Network Identifier, and the last address is reserved as the Broadcast address for communicating with all hosts on that subnet.

What subnet mask does a /24 CIDR prefix represent?

A /24 prefix represents 24 bits of 1s followed by 8 bits of 0s, which converts to decimal 255.255.255.0. It provides 256 total IP addresses and 254 usable host addresses.

What are the RFC 1918 private IPv4 address ranges?

The three private address blocks reserved for local networks are: 10.0.0.0/8 (10.0.0.0 – 10.255.255.255), 172.16.0.0/12 (172.16.0.0 – 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 – 192.168.255.255).

Is this calculation performed locally in my browser?

Yes. All IP conversions, bitwise AND/OR operations, and range calculations are computed client-side using JavaScript.

IPv4 CIDR Subnet Calculator

Calculate IPv4 CIDR subnet ranges, usable host IPs, network and broadcast addresses, and netmasks online.

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Common Subnet Presets:

IPv4 Address

CIDR Prefix: /24 (255.255.255.0)

Subnet Block

192.168.1.0/24

🔒 Private (RFC 1918)Class C

Subnet Netmask:255.255.255.0

Wildcard Mask:0.0.0.255

Network IP:192.168.1.0

Broadcast IP:192.168.1.255

First Usable IP:192.168.1.1

Last Usable IP:192.168.1.254

Usable Hosts:254

Total IP Range:256 addresses

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About IPv4 CIDR Subnet Calculator

The IPv4 CIDR Subnet Calculator provides instant networking calculations for systems administrators, cloud architects, and DevOps engineers configuring VPCs, routers, and firewalls. Simply provide an IPv4 address and CIDR prefix (from /1 to /32) to compute subnet masks, wildcard masks, network boundaries, and exact usable IP ranges.

How to use IPv4 CIDR Subnet Calculator

Enter an IPv4 address (e.g. 192.168.1.0 or 10.0.0.1).
Select or enter a CIDR prefix length (e.g. /24, /16, /28).
Review the calculated Network Address, Broadcast Address, and Subnet Mask.
Inspect the first and last usable host IPs and total available host count.

Key features

Full CIDR prefix range support from /1 (supernet) up to /32 (single host)
Computes Subnet Mask, Wildcard Inverse Mask, Network, and Broadcast IPs
Calculates total IP count and usable host count excluding network & broadcast
Detects private RFC 1918 address space and IPv4 address classes (A, B, C)

Frequently asked questions

What is CIDR notation?: CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated routing prefix using a slash followed by the number of leading 1-bits in the subnet mask (e.g. 192.168.1.0/24 means the first 24 bits belong to the network prefix).
Why are there 2 fewer usable hosts than total IP addresses in a subnet?: In standard IPv4 subnets (prefix /30 and lower), the very first address in the block is reserved as the Network Identifier, and the last address is reserved as the Broadcast address for communicating with all hosts on that subnet.
What subnet mask does a /24 CIDR prefix represent?: A /24 prefix represents 24 bits of 1s followed by 8 bits of 0s, which converts to decimal 255.255.255.0. It provides 256 total IP addresses and 254 usable host addresses.
What are the RFC 1918 private IPv4 address ranges?: The three private address blocks reserved for local networks are: 10.0.0.0/8 (10.0.0.0 – 10.255.255.255), 172.16.0.0/12 (172.16.0.0 – 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 – 192.168.255.255).
Is this calculation performed locally in my browser?: Yes. All IP conversions, bitwise AND/OR operations, and range calculations are computed client-side using JavaScript.