IPv4 CIDR Calculator
Enter an IP and CIDR prefix (or type CIDR directly like 192.168.1.10/24) to calculate subnet details instantly.
Why an IP CIDR Calculator Is Useful
If you work with routers, cloud instances, VLANs, firewalls, or even home lab equipment, you eventually need to answer questions like: “What is the network address?”, “How many hosts can this subnet support?”, and “What is the broadcast address?”. An IP CIDR calculator solves these in seconds.
CIDR (Classless Inter-Domain Routing) replaced older class-based addressing and made subnetting more flexible. Instead of rigid class A/B/C network boundaries, CIDR lets you define exact network sizes using a prefix length such as /24, /27, or /30.
Quick CIDR Fundamentals
What does “/24” mean?
In 192.168.10.0/24, the /24 means the first 24 bits identify the network and the remaining
8 bits identify hosts. More network bits = fewer host bits, which means smaller subnets.
Subnet mask relationship
Every CIDR prefix maps to a subnet mask:
- /8 → 255.0.0.0
- /16 → 255.255.0.0
- /24 → 255.255.255.0
- /30 → 255.255.255.252
CIDR is just a cleaner, shorter way to represent the same mask information.
How to Read the Calculator Output
Network Address
The first address in the subnet. It identifies the subnet itself, not an individual host.
Broadcast Address
The last address in the subnet. In traditional IPv4 subnetting, this address is used to send traffic to all hosts in that subnet.
Usable Host Range
The range of assignable host IPs between network and broadcast. Special cases:
- /31: typically used for point-to-point links; both addresses may be usable.
- /32: single-host route (exactly one address).
Common CIDR Blocks at a Glance
- /24 → 256 total addresses, 254 usable hosts
- /25 → 128 total addresses, 126 usable hosts
- /26 → 64 total addresses, 62 usable hosts
- /27 → 32 total addresses, 30 usable hosts
- /28 → 16 total addresses, 14 usable hosts
- /29 → 8 total addresses, 6 usable hosts
- /30 → 4 total addresses, 2 usable hosts
Private IPv4 Ranges (RFC 1918)
These ranges are not publicly routed on the internet and are commonly used in LANs and VPCs:
- 10.0.0.0/8
- 172.16.0.0/12
- 192.168.0.0/16
Knowing whether an address is private or public helps during NAT, VPN, and peering design.
Practical Examples
Example 1: 192.168.50.23/27
A /27 has 32 addresses per block. The subnet containing .23 starts at .0 and ends at .31. Usable hosts are .1 through .30.
Example 2: 10.12.8.200/20
A /20 uses 16-address steps in the third octet. The matching network is 10.12.0.0/20, and the broadcast is 10.12.15.255.
Subnetting Tips for Real Environments
- Leave growth room when sizing subnets for production services.
- Use consistent subnet boundaries across regions or sites.
- Document VPC/VNet CIDRs to avoid overlap during peering.
- Use /31 and /32 only where your platform and routing design support them.
- Validate ACL and firewall rules against network/broadcast boundaries.
Final Thoughts
A dependable IP CIDR calculator saves time and prevents addressing mistakes that can cause hard-to-diagnose outages. Use the tool above whenever you need fast subnet math, clear host ranges, and accurate mask conversion. It is ideal for students learning networking, administrators troubleshooting connectivity, and engineers planning scalable IP designs.