CIDR Subnet Calculator
Enter any CIDR notation (e.g. 192.168.1.0/24) to get network address, broadcast, subnet mask, and usable host count.
A CIDR calculator (Classless Inter-Domain Routing) breaks an IP range like 192.168.1.0/24 into its network address, broadcast address, subnet mask, and usable host count. The /24 notation means 24 bits are fixed, leaving 8 bits for hosts — 256 addresses total, 254 usable. ToolHub Pro's free CIDR subnet calculator works out network, broadcast, host range, and usable hosts for any IPv4 CIDR block instantly.
Subnet details will appear here.
IP Addresses and Subnets
An IPv4 address is a 32-bit number written as four decimal octets (e.g. 192.168.1.0). A subnet divides a larger network into smaller logical segments, allowing you to control broadcast domains and network routing. Subnets are defined by a network address and a subnet mask — the mask determines which part of the IP address identifies the network and which part identifies individual hosts. Understanding subnets is essential for configuring firewalls, cloud VPCs (Virtual Private Clouds), and network security groups where you need to specify which IP ranges are allowed or denied.
CIDR Notation Explained
CIDR (Classless Inter-Domain Routing) notation writes the network address followed by a slash and the number of network bits: 192.168.1.0/24. The /24 means the first 24 of 32 bits are the network portion, leaving 8 bits for host addresses, supporting 256 addresses (254 usable, excluding network and broadcast). /16 gives 65,536 addresses; /32 is a single host. CIDR replaced the old Class A/B/C system and allows more flexible allocation of address space.
Common Subnet Sizes
For practical reference: /32 = 1 host (single IP rules in firewalls), /30 = 2 usable hosts (point-to-point links), /28 = 14 hosts, /24 = 254 hosts (standard office LAN), /16 = 65,534 hosts (large VPC), /0 = all IP addresses ("allow from anywhere" in security group rules). AWS VPCs typically use /16 as the VPC CIDR and /24 subnets for individual availability zones, giving room for 256 subnets per VPC.
Private Address Ranges
Three IP ranges are reserved for private networks and are never routed on the public internet: 10.0.0.0/8 (16.7M addresses, common in large cloud VPCs), 172.16.0.0/12 (1M addresses, Docker's default), and 192.168.0.0/16 (65,536 addresses, typical home/office routers). When configuring security groups or firewall rules to allow internal traffic only, these ranges are used to restrict access to within the private network. Traffic between these ranges never crosses the public internet, but still requires routing within a data centre or cloud environment.
Sources
ToolHub Pro Editorial Team
Security Standards Reviewers · verified against NIST & IETF standards
Security tools are implemented and checked against published specifications, including NIST SP 800-63B password guidelines, FIPS 140-3 cryptographic module requirements, and the IETF RFCs covering encoding, hashing and key generation (RFC 4648, RFC 6234). Referenced standards are listed on each tool page.
Reviewed by ToolHub Pro Editorial Team, reviewed implementations against NIST, FIPS & IETF references
Editorial standards →Frequently Asked Questions
What does /24 mean in CIDR notation?
What is the difference between network and broadcast address?
What CIDR notation is used for single hosts?
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