CIDR/Subnet Calculator - Free IP Range Calculator
Calculate network addresses, subnet masks, usable IP ranges, broadcast addresses, and split networks into smaller subnets. Essential for AWS VPC planning, cloud infrastructure design, and network engineering. Free, instant, and private.
IP Range Visualization
Subnet Information
Common Subnet Sizes
Binary Subnet Mask
Split into Smaller Subnets
... and 240 more subnets
AWS VPC Reserved IPs
AWS reserves 5 IP addresses in each subnet:
- .0 - Network address
- .1 - VPC router
- .2 - DNS server
- .3 - Reserved for future use
- .255 - Broadcast (not supported in VPC)
What You Get
Network Calculations
- Network address identification
- Broadcast address calculation
- First and last usable IP
- Total and usable IP count
- Binary representation
Subnet Mask Details
- Dotted decimal notation
- CIDR prefix length
- Wildcard mask (inverse)
- Subnet class identification
- Private/public range detection
Subnet Splitting
- Split into equal subnets
- Custom prefix selection
- Subnet range visualization
- AWS VPC subnet planning
- Network hierarchy display
How to Use This Tool
Enter CIDR Block
Type a CIDR notation like 10.0.0.0/16 or just an IP address with prefix length
Calculate
Click Calculate to see network details, IP ranges, and subnet information
Split or Copy
Use the subnet splitter to divide into smaller blocks or copy results
Common CIDR Blocks Reference
| CIDR | Subnet Mask | Total IPs | Usable IPs | Use Case |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 | Large enterprise network |
| /16 | 255.255.0.0 | 65,536 | 65,534 | AWS VPC (max recommended) |
| /20 | 255.255.240.0 | 4,096 | 4,094 | Large subnet / department |
| /24 | 255.255.255.0 | 256 | 254 | Standard subnet (most common) |
| /28 | 255.255.255.240 | 16 | 14 | Small/NAT/bastion subnet |
| /32 | 255.255.255.255 | 1 | 1 | Single host (security groups) |
Why CIDR and Subnet Planning Matters
Proper CIDR planning is essential for cloud infrastructure. In AWS, Azure, and GCP, your VPC CIDR block determines how many resources you can deploy and how your network segments are organized. Poor planning leads to IP exhaustion and complex routing.
Subnet sizing affects security and scalability. Smaller subnets provide better isolation for security groups and network ACLs, while larger subnets offer more flexibility for auto-scaling groups and container orchestration.
Understanding CIDR notation is crucial for configuring security groups, firewall rules, and access control lists. A /32 represents a single IP, while /0 means all IP addresses - getting these wrong can expose your infrastructure to attacks.
Network troubleshooting requires understanding IP ranges. Knowing if two IPs are in the same subnet helps diagnose routing issues, security group problems, and connectivity failures in complex multi-tier architectures.
Frequently Asked Questions
CIDR (Classless Inter-Domain Routing) notation is a compact way to represent an IP address and its associated network mask. It uses a format like 192.168.1.0/24, where the number after the slash indicates how many bits of the address are used for the network portion. A /24 means the first 24 bits are the network address, leaving 8 bits (256 addresses) for hosts.