CIDR → Subnet Mask Converter
Convert CIDR notation to subnet mask format
Subnet Mask 255.255.255.0
Subnet Information
Network Bits 24
Host Bits 8
Usable Hosts 254
Common Subnets
Understanding CIDR and Subnet Masks
CIDR Notation
CIDR (Classless Inter-Domain Routing) uses a slash followed by a number (e.g., /24) to indicate how many bits are used for the network portion of an IP address.
Subnet Mask
A 32-bit number that masks an IP address to divide it into network and host portions. Written in dotted decimal notation (e.g., 255.255.255.0).
Network Bits
The leftmost bits in an IP address that identify the network. More network bits mean smaller subnets with fewer available host addresses.
Host Bits
The remaining bits used for host addresses within the network. More host bits allow for more devices but fewer possible subnets.
Common Conversions
/24 ↔ 255.255.255.0 254 hosts
/25 ↔ 255.255.255.128 126 hosts
/26 ↔ 255.255.255.192 62 hosts
/30 ↔ 255.255.255.252 2 hosts
🔧 Usage Tips
- Smaller CIDR = Bigger Network: /16 has more hosts than /24
- Binary Thinking: Each bit doubles or halves the number of addresses
- /30 for Links: Perfect for point-to-point connections (only 2 usable IPs)
- Planning: Start with larger subnets and subdivide as needed