IP Subnet Calculator

IPv4 CIDR Subnetting
Anish Nath
Calculate Subnet
IP Address / CIDR
Enter IP with CIDR prefix (e.g., 10.0.0.0/8, 172.16.0.0/16)
CIDR Prefix: /24
/8 (16M hosts) /16 (65K) /24 (254) /30 (2)
Common Subnets
Options
CIDR Quick Reference
CIDRSubnet MaskHosts
/8255.0.0.016,777,214
/16255.255.0.065,534
/24255.255.255.0254
/25255.255.255.128126
/26255.255.255.19262
/27255.255.255.22430
/28255.255.255.24014
/29255.255.255.2486
/30255.255.255.2522
Subnet Information

Subnet information will appear here

Enter a CIDR address and click Calculate
CLI Commands
Linux: Calculate subnet with ipcalc
$ ipcalc 192.168.1.0/24
Windows: Show IP configuration
C:\> ipconfig /all
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FAQs

How many usable hosts are in a subnet?
Usable hosts = total IPs minus network and broadcast. /24 → 254 usable; /28 → 14 usable.
Which private ranges should I use?
RFC1918: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Avoid overlaps across environments.
What is a wildcard mask?
Wildcard is inverse of subnet mask; used in ACLs. For 255.255.255.0, wildcard is 0.0.0.255.
Understanding IP Subnetting
What is Subnetting?

Subnetting is the practice of dividing a network into smaller, more manageable sub-networks (subnets). This improves network performance, security, and simplifies administration. Each subnet has its own network address, broadcast address, and range of usable host addresses.

CIDR Notation Explained

CIDR (Classless Inter-Domain Routing) notation combines an IP address with its subnet mask in a compact format: 192.168.1.0/24. The number after the slash indicates how many bits are used for the network portion (prefix length).

Network Address

The first address in a subnet, where all host bits are 0. It identifies the network itself and cannot be assigned to a host.

Broadcast Address

The last address in a subnet, where all host bits are 1. Packets sent here reach all hosts on the subnet.

RFC 1918 Private Address Ranges
RangeCIDRAddressesTypical Use
10.0.0.0 - 10.255.255.25510.0.0.0/816,777,216Large enterprises, data centers
172.16.0.0 - 172.31.255.255172.16.0.0/121,048,576Medium organizations
192.168.0.0 - 192.168.255.255192.168.0.0/1665,536Home networks, small offices
Subnet Calculation Formula
  • Number of subnets: 2(borrowed bits)
  • Hosts per subnet: 2(host bits) - 2
  • Host bits: 32 - prefix length
  • Wildcard mask: 255.255.255.255 - subnet mask
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