CIDR Calculator

Calculate subnet masks, IP ranges, network addresses, and more from CIDR notation. Instant results in your browser.

How it works: Enter an IP address with CIDR prefix (e.g., 192.168.1.0/24). The calculator instantly shows network address, broadcast, host range, subnet mask, and binary representation.

Network Information

Network Address
192.168.1.0
Broadcast Address
192.168.1.255
Subnet Mask
255.255.255.0
Wildcard Mask
0.0.0.255
Prefix Length
/24

Host Range

First Usable Host
192.168.1.1
Last Usable Host
192.168.1.254
Usable Hosts
254
IP Class
Class C
Private Range
Yes

Binary Representation

IP Address11000000.10101000.00000001.00000000
Subnet Mask11111111.11111111.11111111.00000000

Common Subnet Quick Reference

CIDRSubnet MaskHosts
/8255.0.0.016,777,214Class A
/16255.255.0.065,534Class B
/24255.255.255.0254Class C
/25255.255.255.128126
/26255.255.255.19262
/27255.255.255.22430
/28255.255.255.24014
/29255.255.255.2486
/30255.255.255.2522Point-to-point
/31255.255.255.2542RFC 3021
/32255.255.255.2551Host route

What is CIDR Notation?

CIDR (Classless Inter-Domain Routing) notation is a compact way to represent an IP address and its associated network mask. Written as IP/prefix (e.g., 192.168.1.0/24), the number after the slash indicates how many bits of the address identify the network. The remaining bits identify individual hosts. CIDR replaced the older classful addressing system (Class A, B, C) to allow more flexible allocation of IP addresses.

How Subnet Masks Work

A subnet mask divides an IP address into network and host portions. In binary, the mask consists of consecutive 1s (network bits) followed by consecutive 0s (host bits). For example, /24 means 24 network bits and 8 host bits, giving 255.255.255.0 as the subnet mask. The number of host bits determines how many devices can exist on the subnet: 2^host_bits - 2 (subtracting network and broadcast addresses).

Common Subnet Sizes

The most common subnets are /24 (256 addresses, 254 usable hosts — typical for small networks), /16 (65,536 addresses — medium organizations), and /8 (16 million addresses — large ISPs). For point-to-point links between routers, /30 (4 addresses, 2 usable) or /31 (2 addresses, RFC 3021) is standard. Cloud providers like AWS use /16 for VPCs and /24 for subnets by default.

CIDR Tips for Network Design

  • Always plan for growth — choose a subnet larger than you currently need
  • Use /24 for most LAN segments (254 hosts is usually sufficient)
  • Use /30 or /31 for point-to-point links between routers
  • Private ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
  • Avoid overlapping subnets when connecting networks via VPN
  • Document your IP allocation plan — subnet sprawl causes routing nightmares