CIDR Calculator

Calculate subnet details from CIDR notation. Find IP ranges, usable hosts, subnet masks, and network boundaries. Essential for network planning and troubleshooting.

CIDR Notation

Enter IP address with prefix (e.g., 10.0.0.0/8)

Common Subnets

Prefix to Hosts Reference

Prefix	Subnet Mask	Hosts	Use Case
/8	255.0.0.0	16,777,214	Large enterprise
/16	255.255.0.0	65,534	Campus/large site
/24	255.255.255.0	254	Standard LAN
/25	255.255.255.128	126	Small office
/26	255.255.255.192	62	Department
/27	255.255.255.224	30	Small team
/28	255.255.255.240	14	Very small
/30	255.255.255.252	2	Point-to-point
/32	255.255.255.255	1	Single host

Subnet Details

Network Address
Broadcast Address
First Usable IP
Last Usable IP
Usable Hosts
Total IPs
Subnet Mask
Wildcard Mask
Binary Mask
IP Class
IP Type

IP Range

Subnet Breakdown

Network bits:

Host bits:

Visual:

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Frequently Asked Questions

CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length: 192.168.1.0/24. The /24 means the first 24 bits are the network portion, leaving 8 bits for hosts.

Hosts = 2^(32-prefix) - 2. The -2 accounts for network address and broadcast. A /24 has 2^8 - 2 = 254 usable hosts. A /16 has 65,534 hosts.

A subnet mask identifies the network vs host portion of an IP. /24 = 255.255.255.0. Each octet of 255 means those 8 bits are network bits.

Wildcard mask is the inverse of subnet mask, used in ACLs and routing. For /24 (255.255.255.0), wildcard is 0.0.0.255. Calculate: 255.255.255.255 - subnet mask.

Network address is the first IP (all host bits 0), used to identify the subnet. Broadcast address is the last IP (all host bits 1), used to reach all hosts on the subnet.

Increase the prefix length. A /24 split into 4 subnets becomes four /26 networks. Each /26 has 62 usable hosts instead of 254.

/24 gives 254 hosts in one network. /25 gives two networks with 126 hosts each. More prefix bits = smaller subnets with fewer hosts.

Combining multiple smaller networks into one larger block. Four /24 networks can become one /22 if they're contiguous. Reduces routing table entries.

Apply the subnet mask to both the IP and network address using AND. If results match, the IP is in the subnet. This tool shows the range for easy checking.

RFC 1918 private ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. These are not routed on the public internet and free to use internally.

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