IP Subnet Calculator
Calculate subnet information from CIDR notation. Find network addresses, broadcast addresses, usable IP ranges, and subnet masks.
Enter CIDR Notation
Common prefixes:
CIDR Reference Table
| CIDR | Subnet Mask | Hosts | Usable |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2* |
| /32 | 255.255.255.255 | 1 | 1 |
* /31 is a special case for point-to-point links (RFC 3021)
Understanding Subnets
Subnetting divides a large network into smaller, more manageable pieces. Each subnet has its own range of IP addresses, allowing for better organization, security, and efficient use of IP addresses.
The CIDR prefix (like /24) indicates how many bits are used for the network portion of the address. The remaining bits are used for host addresses.
Private IP Ranges
10.0.0.0/8
Class A private - 16.7 million addresses
172.16.0.0/12
Class B private - 1 million addresses
192.168.0.0/16
Class C private - 65,536 addresses
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation is a compact way to represent IP addresses and their associated network prefixes. For example, 192.168.1.0/24 represents a network with 256 addresses (254 usable) starting from 192.168.1.0.
What is a subnet mask?
A subnet mask defines which portion of an IP address identifies the network and which identifies the host. For example, 255.255.255.0 (/24) means the first three octets identify the network, and the last octet identifies the host.
Why are there fewer usable hosts than total hosts?
Two addresses are reserved in each subnet: the network address (first address) used to identify the network, and the broadcast address (last address) used to send messages to all hosts on the network.
What is the difference between private and public IP ranges?
Private IP ranges (10.x.x.x, 172.16-31.x.x, 192.168.x.x) are reserved for internal networks and cannot be routed on the internet. Public IPs are globally unique and routable on the internet.