What is an IP address CIDR calculator?
An IP address CIDR calculator helps you quickly convert an IPv4 address and prefix (like /24) into practical network details: subnet mask, network address, broadcast address, usable host range, and more. Instead of calculating bit boundaries manually, you can enter one line and get accurate subnetting results instantly.
This is useful for network engineers, sysadmins, cloud architects, developers, students preparing for certification exams, and anyone planning VLANs or firewall rules.
How CIDR works in plain language
CIDR stands for Classless Inter-Domain Routing. The prefix value after the slash indicates how many bits are reserved for the network portion of the address.
- /8 means first 8 bits are network bits.
- /16 means first 16 bits are network bits.
- /24 means first 24 bits are network bits.
- /30, /31, /32 are often used for special link and host use cases.
The remaining bits are host bits. More host bits means more addresses in that subnet.
What this calculator returns
Core subnet values
- Subnet Mask: Decimal form of the prefix (for example, /24 = 255.255.255.0)
- Wildcard Mask: Inverse of subnet mask, often used in ACL configurations
- Network Address: First address in the subnet
- Broadcast Address: Last address in the subnet
- Usable Host Range: First and last usable host addresses
Helpful classification values
- Address Class: A/B/C/D/E classification based on first octet
- Address Type: Whether the IP is private or public
- Binary Display: Binary form of IP and mask for deeper subnet analysis
Examples you can try
- 192.168.1.10/24 → common home/office subnet
- 10.20.30.40/16 → larger private enterprise range
- 172.16.8.5/20 → mid-size segmented network
- 203.0.113.9/30 → point-to-point style small subnet
- 198.51.100.7/32 → single-host route
Quick subnet reference (IPv4)
- /24 = 256 total addresses, 254 usable hosts
- /25 = 128 total addresses, 126 usable hosts
- /26 = 64 total addresses, 62 usable hosts
- /27 = 32 total addresses, 30 usable hosts
- /28 = 16 total addresses, 14 usable hosts
- /29 = 8 total addresses, 6 usable hosts
- /30 = 4 total addresses, 2 usable hosts
- /31 = 2 total addresses (commonly used on point-to-point links)
- /32 = 1 total address (host route)
Common mistakes this tool helps prevent
- Using the wrong subnet mask for a prefix length
- Assigning the network or broadcast address to a host
- Misreading usable host range after subnetting
- Incorrect ACL wildcard masks
- Planning subnets that do not have enough hosts
When to use a CIDR calculator
Use a CIDR calculator anytime you design or troubleshoot networks: cloud VPC planning, office LAN segmentation, VPN tunnel endpoints, static routes, firewall policies, and IPAM documentation. It saves time and reduces error, especially when working quickly under operational pressure.