IP Subnet Calculator — CIDR & Subnet Mask Calculator

Convert between CIDR and subnet mask, compute network & broadcast addresses, usable hosts, wildcard mask, and more.

Definition

An IP Subnet Calculator helps network engineers and IT pros convert CIDR notation to subnet mask, calculate network and broadcast addresses, and determine the usable host range for IPv4 subnets.

Key Features

Convert between CIDR (e.g. /24) and dotted subnet mask (e.g. 255.255.255.0)
Calculate network, broadcast, first/last usable host
Number of hosts and usable hosts (special handling for /31 & /32)
Wildcard mask, binary mask view, and next subnet

How to Use (step-by-step)

Type an IPv4 address with CIDR (e.g. 192.168.0.5/26) or IP followed by a subnet mask (10.0.0.1 255.255.255.192).
Click Calculate. Results will appear in the Results box.
Use Use Example to load sample input. Click Clear to reset.

Real-World Use Cases

Planning IP address allocation for VLANs and subnets
Configuring router and firewall interfaces
Troubleshooting network addressing issues

Benefits

Save time and reduce configuration mistakes
Clear, human-readable output for documentation
Portable and lightweight — no libraries required

FAQ

Q: What is CIDR?: CIDR (Classless Inter-Domain Routing) expresses the network prefix length like /24, meaning the first 24 bits are network bits.
Q: How do I convert a mask to CIDR?: Count the number of 1 bits in the subnet mask. For example, 255.255.255.0 has 24 ones → /24.
Q: What are usable hosts?: Most subnets reserve network and broadcast addresses; usable hosts = 2^(32−CIDR) − 2. Exceptions: /31 (two addresses for point-to-point per RFC 3021) and /32 (single host).
Q: Can I paste multiple inputs?: This simple UI accepts a single input at a time. You may run multiple calculations sequentially. (Advanced bulk mode can be added on request.)
Q: Is IPv6 supported?: Not in this version — it focuses on IPv4. IPv6 support can be implemented separately.