cidr ip range calculator - Aaron Graves, PhDude Replica

The CIDR IP range calculator below helps you instantly convert an IPv4 address and prefix into a complete subnet summary. Whether you are planning VLANs, troubleshooting an ACL, or preparing firewall rules, this tool gives you the exact network address, broadcast address, host range, subnet mask, wildcard mask, and usable host counts.

What is CIDR?

CIDR stands for Classless Inter-Domain Routing. It is a modern way to represent IP networks using a compact IP/prefix format, such as 192.168.1.0/24. The number after the slash indicates how many bits are reserved for the network portion.

Before CIDR, networks relied heavily on fixed class boundaries (Class A, B, C). CIDR improved efficiency by allowing variable-length subnet masks (VLSM), reducing wasted addresses and making route aggregation far more practical on the internet.

CIDR Notation in One Line

/8 means 8 network bits, 24 host bits.
/24 means 24 network bits, 8 host bits.
/30 means 30 network bits, 2 host bits.
/32 means a single host address.

How to use this CIDR IP range calculator

Enter an IPv4 address (example: 172.16.8.77).
Enter prefix length from 0 to 32.
Click Calculate Range.
Read your network details in the result panel.

You can also type the full CIDR in the IP field (for example, 10.20.30.40/19), and the calculator will parse it automatically.

What the results mean

Network Address

The first address in the subnet. Routers use this value to identify the subnet itself.

Broadcast Address

The last address in the subnet. Traditionally used for one-to-all communication in that subnet.

First and Last Usable Host

This is the practical host range for assigning to devices. For standard subnets, these exclude network and broadcast addresses. For /31, both addresses are often usable in point-to-point links.

Subnet Mask and Wildcard Mask

The subnet mask defines network bits (e.g., 255.255.255.0). The wildcard mask is the inverse (e.g., 0.0.0.255), commonly used in ACLs and route filters.

Common CIDR blocks at a glance

/24 → 256 total addresses (254 usable)
/25 → 128 total addresses (126 usable)
/26 → 64 total addresses (62 usable)
/27 → 32 total addresses (30 usable)
/28 → 16 total addresses (14 usable)
/29 → 8 total addresses (6 usable)
/30 → 4 total addresses (2 usable)
/31 → 2 total addresses (often both usable for point-to-point)
/32 → 1 address (single host route)

Practical scenarios

Subnet planning

Need separate segments for users, servers, and printers? CIDR lets you size each segment intentionally so you keep growth room without wasting address space.

Firewall and ACL rules

When creating security policies, you often need exact network and wildcard boundaries. Wrong boundaries can allow too much or block critical traffic.

Cloud and hybrid networking

In AWS, Azure, GCP, and on-prem environments, CIDR overlap is a frequent problem. Fast subnet calculations help avoid peering and routing conflicts early.

Frequent mistakes to avoid

Assuming all subnets use classful defaults like /24 or /16.
Forgetting that usable host math changes for /31 and /32.
Mixing up subnet mask and wildcard mask in ACL configurations.
Ignoring overlap checks when merging branch or cloud networks.

Final thoughts

A reliable CIDR calculator is one of the most useful tools in day-to-day networking. Use this page when you need fast, accurate IPv4 subnet details without opening a spreadsheet or memorizing bit boundaries. Bookmark it for subnetting, route design, and troubleshooting sessions.