CIDR Calculator Online
Enter a CIDR block (e.g., 192.168.1.0/24) and instantly see the network address, broadcast address, subnet mask, and total host count. All calculations happen in your browser.
IP / CIDR Toolkit
Subnet calculator, VLSM divider, IP range converter, and IP address classifier — all in one toolkit.
Common Subnets
▶CIDR Reference Table
| CIDR | Subnet Mask | Addresses | Usable Hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /9 | 255.128.0.0 | 8,388,608 | 8,388,606 |
| /10 | 255.192.0.0 | 4,194,304 | 4,194,302 |
| /11 | 255.224.0.0 | 2,097,152 | 2,097,150 |
| /12 | 255.240.0.0 | 1,048,576 | 1,048,574 |
| /13 | 255.248.0.0 | 524,288 | 524,286 |
| /14 | 255.252.0.0 | 262,144 | 262,142 |
| /15 | 255.254.0.0 | 131,072 | 131,070 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /17 | 255.255.128.0 | 32,768 | 32,766 |
| /18 | 255.255.192.0 | 16,384 | 16,382 |
| /19 | 255.255.224.0 | 8,192 | 8,190 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /21 | 255.255.248.0 | 2,048 | 2,046 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 512 | 510 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 |
| /32 | 255.255.255.255 | 1 | 1 |
About Subnet Calculation
- CIDR notation combines an IP address with a prefix length (e.g.,
192.168.1.0/24). - The prefix length defines how many bits are the network portion — the rest are host bits.
- Network address = all host bits set to 0. Broadcast = all host bits set to 1.
- Usable hosts = total addresses minus network and broadcast (except /31 and /32 special cases).
- Private ranges (RFC 1918): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.
- Everything runs in your browser — no data is sent over the network.
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation represents IP address ranges using a base address and prefix length, such as 10.0.0.0/8. The prefix length indicates how many leading bits define the network portion. CIDR replaced the old classful addressing system (Class A, B, C) in 1993, enabling more efficient allocation of IP address space and smaller routing tables.
Common use cases
Network engineers use CIDR calculators to plan subnets for cloud VPCs (AWS, Azure, GCP), configure firewall rules, set up VPN tunnels, and design office network layouts. DevOps teams reference CIDR blocks when writing security group rules, Kubernetes network policies, and infrastructure-as-code definitions in Terraform or CloudFormation.
Frequently Asked Questions
How many hosts are in a /24 network?
A /24 network has 256 total IP addresses (2^8). Subtracting the network address and broadcast address leaves 254 usable host addresses. This is the most common subnet size for small LANs.
What is the difference between CIDR and a subnet mask?
They represent the same information in different formats. CIDR notation /24 is equivalent to the subnet mask 255.255.255.0. CIDR is more compact and commonly used in modern networking, routing tables, and cloud configurations.