Calculate network information from CIDR notation
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Type an IP address with CIDR suffix (192.168.1.0/24) to instantly calculate network properties. CIDR notation uses /prefix length where /24 means 24 bits for network, 8 bits for hosts.
See calculated network address, broadcast address, subnet mask, wildcard mask, usable host range, and total hosts. Essential for subnet design, firewall rules, and network documentation.
Enter how many subnets you need to split the network into. The calculator shows optimal CIDR notation, hosts per subnet, and individual subnet ranges for network planning.
Click copy buttons for subnet mask, network address, or host ranges. Use these values in router configs, firewall rules, DHCP servers, or network documentation.
Understanding CIDR subnet calculations
CIDR (Classless Inter-Domain Routing) is the standard notation for defining IP address ranges and subnets in modern networking. Introduced in 1993 to replace wasteful classful addressing (Class A, B, C), CIDR uses a slash notation (/24, /16, /8) to specify how many bits of an IP address represent the network versus host portions. Understanding CIDR is essential for cloud infrastructure, Kubernetes networking, AWS VPC design, firewall configuration, and any network architecture work.
CIDR notation combines an IP address with a prefix length: 192.168.1.0/24. The /24 means the first 24 bits identify the network, leaving 8 bits for hosts. This /24 subnet contains 256 IP addresses (2^8 = 256), with 254 usable for hosts after subtracting network and broadcast addresses. Smaller prefix numbers mean larger networks: /16 has 65,536 IPs, /8 has 16.7 million IPs. Larger prefix numbers mean smaller networks: /30 has only 4 IPs (2 usable), /32 is a single IP.
Cloud platforms like AWS VPC, Google Cloud, and Azure require CIDR notation for network configuration. When creating a VPC, you specify a CIDR block (10.0.0.0/16) that defines the available IP space. Subnets within the VPC use smaller CIDR blocks (10.0.1.0/24, 10.0.2.0/24) carved from the VPC range. Incorrect CIDR planning causes IP exhaustion, overlapping subnets, or insufficient address space for scaling.
Kubernetes networking relies heavily on CIDR for pod and service IP allocation. Pod CIDR defines the IP range for pod IPs, service CIDR defines cluster service IPs, and node CIDR defines node network ranges. Overlapping CIDRs between clusters, pods, and services break networking. Multi-cluster deployments require careful CIDR planning to avoid conflicts.
Firewall rules and security groups use CIDR to specify allowed/denied IP ranges. Instead of individual IPs, you grant access to entire subnets (10.0.1.0/24 for internal servers) or restrict to specific ranges (203.0.113.0/29 for office IPs). CIDR-based rules are more maintainable than long lists of individual IPs and scale better.
CIDR is the modern shorthand for subnet masks. A /24 CIDR equals subnet mask 255.255.255.0, /16 equals 255.255.0.0, /8 equals 255.0.0.0. CIDR is more concise and flexible than traditional classful addressing (Class A, B, C) because it allows arbitrary prefix lengths. You can have a /22 subnet (between Class B and C) for exactly the IP count you need without wasting addresses.
Private IP ranges (RFC 1918) are used for internal networks and not routable on the internet:
Public IP addresses are routable on the internet and must be globally unique. Cloud providers allocate public IPs from their owned ranges. On-premises data centers lease public IPs from ISPs or regional internet registries (ARIN, RIPE, APNIC).
Overlapping subnets: Creating subnet 10.0.1.0/24 and later adding 10.0.0.0/16 causes overlap. The /16 contains the /24. Always check existing subnets before allocating new ones.
IP exhaustion: Starting with a /24 (254 hosts) for a VPC that grows to 1,000 servers. Plan for growth: use /16 for VPCs, subnet into smaller /24 or /22 ranges for flexibility.
Broadcast address misuse: The last IP in a subnet (.255 in /24) is broadcast and cannot be assigned to hosts. CIDR calculators show usable ranges excluding network and broadcast IPs.
Security group CIDR typos: Opening firewall to 0.0.0.0/0 (entire internet) instead of 10.0.0.0/8 (internal network) creates security vulnerabilities. Double-check CIDR in production security rules.
How developers use CIDR calculations
Plan AWS VPC CIDR blocks and subnet allocation for multi-tier applications. Design non-overlapping subnets for public, private, and database tiers across multiple availability zones with room for future growth.
Configure Kubernetes cluster networking with non-overlapping CIDR ranges for pods, services, and nodes. Proper CIDR allocation prevents IP conflicts in multi-cluster environments and enables cluster federation.
Write CIDR-based firewall rules that grant access to specific networks while blocking others. Use CIDR ranges instead of individual IPs for maintainable security policies that scale with infrastructure growth.
Configure Docker bridge networks and overlay networks with custom CIDR ranges. Avoid conflicts with existing network infrastructure by choosing non-overlapping CIDR blocks for container networking.
Master subnet calculations
This CIDR calculator provides instant subnet calculations for network planning, VPC design, and firewall configuration. Enter any valid IPv4 address with CIDR notation to see network properties, usable host ranges, and subnet breakdown.
Enter an IP address with CIDR prefix length (192.168.1.0/24) in the input field. The calculator instantly displays: Network Address (first IP in the subnet), Broadcast Address (last IP in the subnet), Subnet Mask (dotted decimal notation), Wildcard Mask (inverse of subnet mask, used in Cisco ACLs), Usable Host Range (IPs you can assign to devices, excluding network and broadcast), and Total Hosts (usable IP count).
You can enter the IP in any position within the subnet (192.168.1.50/24) and the calculator determines the network address (192.168.1.0). This is useful when you have an existing IP and need to find its subnet boundaries.
The network address is the first IP in the subnet and identifies the network itself (cannot be assigned to hosts). The broadcast address is the last IP and is used for broadcasting to all hosts in the subnet (cannot be assigned). The usable host range is network+1 to broadcast-1, the IPs you can assign to servers, containers, or devices.
For /24 subnets, you lose 2 IPs (network and broadcast) from 256 total, leaving 254 usable. For /30 subnets (4 IPs total), you lose 2, leaving only 2 usable - perfect for point-to-point links. For /31 (RFC 3021), both IPs are usable because network and broadcast are not needed for point-to-point links.
Use the calculator to divide large networks into smaller subnets. For example, start with 10.0.0.0/16 (65,536 IPs) and calculate how many /24 subnets fit: 256 subnets with 254 hosts each. Or divide 192.168.0.0/24 into four /26 subnets: 192.168.0.0/26 (0-63), 192.168.0.64/26 (64-127), 192.168.0.128/26 (128-191), 192.168.0.192/26 (192-255).
Use this calculator when designing AWS VPCs to ensure subnets don't overlap and you have sufficient IP space. When configuring Kubernetes to verify pod CIDR, service CIDR, and node networks don't conflict. When writing firewall rules to determine the correct CIDR range for security groups. When troubleshooting network issues to understand if IPs are in the same subnet or require routing.
Everything you need to know about CIDR
Your network data never leaves your browser
This CIDR calculator operates entirely client-side in your browser. No IP addresses, CIDR ranges, or network configurations are transmitted to any servers. All subnet calculations and IP math happen locally using JavaScript.
Safe for calculating production network ranges, planning AWS VPC architectures, designing Kubernetes cluster networking, or any subnet planning that must remain confidential. Use with confidence for enterprise network design, security group configuration, or infrastructure planning.
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