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CIDR Calculator

Convert between CIDR notation and subnet masks. Enter either a CIDR prefix or subnet mask to get the equivalent.

Results

CIDR Notation:
Subnet Mask:
Network Bits:
Host Bits:

What is CIDR?

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and routing Internet Protocol packets. CIDR notation represents an IP address and its associated network prefix, written as an IP address followed by a slash and the number of network bits.

CIDR vs Subnet Masks

Traditional subnet masks (like 255.255.255.0) can be converted to CIDR notation:

  • 255.255.255.0 = /24
  • 255.255.0.0 = /16
  • 255.0.0.0 = /8

CIDR notation is more compact and flexible, allowing for variable-length subnet masking (VLSM).

How to Use This Calculator

Enter either a CIDR prefix (like /24) or a subnet mask (like 255.255.255.0) in the input field. The calculator will show you the equivalent notation and additional network information.