Calculate CIDR notation, subnet masks, IP ranges, and aggregate networks. Essential tool for network administrators and engineers.
| Prefix | Mask | Addresses |
|---|---|---|
| /32 | 255.255.255.255 | 1 |
| /31 | 255.255.255.254 | 2 |
| /30 | 255.255.255.252 | 4 |
| /29 | 255.255.255.248 | 8 |
| /28 | 255.255.255.240 | 16 |
| /27 | 255.255.255.224 | 32 |
| /26 | 255.255.255.192 | 64 |
| /25 | 255.255.255.128 | 128 |
| /24 | 255.255.255.0 | 256 |
| /23 | 255.255.254.0 | 512 |
| /22 | 255.255.252.0 | 1,024 |
| /21 | 255.255.248.0 | 2,048 |
| /20 | 255.255.240.0 | 4,096 |
| /19 | 255.255.224.0 | 8,192 |
| /18 | 255.255.192.0 | 16,384 |
| /17 | 255.255.128.0 | 32,768 |
| /16 | 255.255.0.0 | 65,536 |
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CIDR (Classless Inter-Domain Routing) is the modern standard for IP address allocation. Our CIDR Calculator helps you convert between CIDR notation and subnet masks, calculate IP ranges, and aggregate networks into supernets. Essential for network planning, firewall configuration, and infrastructure management.
CIDR notation represents IP addresses with their routing prefix (e.g., 192.168.1.0/24). The number after the slash indicates how many bits are used for the network portion. CIDR replaced the old classful addressing system, allowing more flexible allocation of IP addresses and reducing routing table sizes through route aggregation.
CIDR Address Format
IP_Address/Prefix_Length (e.g., 10.0.0.0/8)Convert between CIDR notation and dotted-decimal subnet masks instantly.
Calculate the exact network range, broadcast address, and usable hosts.
Aggregate multiple networks into efficient supernets for route summarization.
See the binary representation to understand how CIDR masking works.
Design efficient network architectures with properly sized subnets.
Create accurate CIDR-based rules for security policies.
Combine multiple routes into supernets to reduce routing table size.
Define VPC subnets and security groups in AWS, Azure, or GCP.
/24 means 24 bits are used for the network portion, leaving 8 bits for hosts. This equals a subnet mask of 255.255.255.0 and provides 256 addresses (254 usable hosts).
The formula is 2^(32-prefix) for total addresses. For usable hosts, subtract 2 (network and broadcast addresses). A /24 has 2^8 = 256 total addresses, or 254 usable hosts.
CIDR (Classless Inter-Domain Routing) is the notation system, while VLSM (Variable Length Subnet Mask) is a technique that uses CIDR to create subnets of different sizes within a network.
Supernetting combines multiple contiguous networks into a single, larger network block. For example, 192.168.0.0/24 and 192.168.1.0/24 can be aggregated into 192.168.0.0/23, reducing routing table entries.
CIDR eliminates the rigid class boundaries (A, B, C) that wasted IP addresses. It allows flexible allocation based on actual needs and enables route aggregation, which reduces internet routing table sizes.