CIDR Calculator
Calculate subnets instantly.
Presets
Network Address
Broadcast Address
Subnet Mask
Wildcard Mask
Usable IP Range
Usable Hosts
IP Class
Binary Notation
11000000.10101000.00000001.00000000Visual Subnet Map
Subnet Split
| # | Network Address | Broadcast Address | Usable Hosts |
|---|---|---|---|
| 1 | 192.168.1.0/26 | 192.168.1.63 | 62 |
| 2 | 192.168.1.64/26 | 192.168.1.127 | 62 |
| 3 | 192.168.1.128/26 | 192.168.1.191 | 62 |
| 4 | 192.168.1.192/26 | 192.168.1.255 | 62 |
Overlap Check
What is CIDR?
CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing Internet Protocol packets. Introduced in 1993 to replace the older classful network design, CIDR is now the standard used across the Internet and all major cloud platforms.
How to Read CIDR Notation
In a CIDR address like "192.168.1.0/24", the number after the slash is the prefix length β the number of bits used for the network portion. A prefix of /24 corresponds to the subnet mask 255.255.255.0, giving you 256 total addresses (254 usable hosts). A smaller prefix means a larger network: /8 can hold over 16 million hosts.
Common Use Cases
- AWS VPC: Start with 10.0.0.0/16 (65,534 hosts) then subdivide into /24 subnets per availability zone
- Home LAN: 192.168.1.0/24 is the most common choice (up to 254 connected devices)
- Docker: 172.17.0.0/16 is the default bridge network used by the Docker daemon
When designing subnets, always plan for growth by choosing a prefix with room to spare. A common pattern in cloud architecture is to allocate a /16 VPC and divide it into /24 subnets per service or availability zone. Keep in mind that cloud providers reserve several IP addresses per subnet for internal use β the exact count varies by provider.
IP Address Classes
- Class A (/8): Large-scale networks like 10.0.0.0/8. Can accommodate over 16 million hosts.
- Class B (/16): Medium-scale networks like 172.16.0.0/12. Supports up to around 1 million hosts.
- Class C (/24): Small networks like 192.168.0.0/24. Up to 254 usable hosts per subnet.
Switch between cloud modes to see how many IPs each provider reserves: AWS reserves 5 per subnet, Azure reserves 5, and GCP reserves 4. Use this during capacity planning to ensure your subnets have enough usable addresses for your workloads. For IPv6, CIDR uses the same slash notation on 128-bit addresses. A /64 prefix is the standard for a single subnet, while ISPs typically delegate /48 blocks to customer sites.