The CIDR to IP Range Converter takes any CIDR block and expands it into its full IP address range — showing you the first IP, last IP, subnet mask, and total host count. Network engineers, security analysts, and cloud architects use this tool to quickly verify firewall rules, audit cloud security groups, and plan IP address allocations without manual calculation.

What Is CIDR Notation?

CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and defining network boundaries. Introduced in RFC 4632, CIDR replaced the older classful addressing system (Class A, B, C) that wasted large portions of the IPv4 address space. A CIDR block is written as an IP address followed by a slash and a prefix length — for example, 192.168.1.0/24. The prefix length indicates how many bits of the address identify the network, with the remaining bits available for host addresses.

How CIDR Works

An IPv4 address is 32 bits long. The prefix length after the slash tells you how many of those bits are fixed (the network portion). The remaining bits define the host range. In 10.0.0.0/8, the first 8 bits are the network prefix, leaving 24 bits for hosts — that is 16,777,216 addresses. A /24 block fixes 24 bits, leaving 8 bits for 256 addresses. The network address is the first address in the range (all host bits set to 0), and the broadcast address is the last (all host bits set to 1). Usable host addresses fall between these two.

Reading CIDR Output

When you enter a CIDR block into this tool, it calculates several values:

First IP (Network Address) — The starting address of the range. No host should be assigned this address in most configurations.
Last IP (Broadcast Address) — The ending address. In traditional networking, this is reserved for broadcast traffic.
Subnet Mask — The dotted-decimal representation of the prefix length (e.g., /24 = 255.255.255.0).
Total Hosts — The total number of addresses in the block, including network and broadcast addresses.

CIDR vs Classful Addressing

Before CIDR, IPv4 networks were divided into rigid classes. A Class C network always had 256 addresses (/24), a Class B had 65,536 (/16), and a Class A had 16.7 million (/8). If an organization needed 500 addresses, they had to request a Class B — wasting over 65,000 addresses. CIDR eliminated this waste by allowing variable-length subnet masking (VLSM), so a /23 block with exactly 512 addresses could be assigned instead. This flexibility was essential to slowing the exhaustion of IPv4 address space.

Common CIDR Block Sizes

Here are frequently encountered CIDR prefix lengths and their address counts:

/32 — 1 address (single host)
/28 — 16 addresses (small office or subnet)
/24 — 256 addresses (standard LAN subnet)
/20 — 4,096 addresses (medium enterprise or cloud VPC subnet)
/16 — 65,536 addresses (large enterprise or legacy Class B)
/8 — 16,777,216 addresses (major ISP or legacy Class A)

Use Cases for CIDR Conversion

Converting CIDR to IP ranges is a routine task in network security and infrastructure management. Firewall rules and access control lists (ACLs) often specify allowed or blocked traffic using CIDR blocks — expanding them to full ranges helps verify that the correct addresses are covered. Cloud security groups in AWS, Azure, and GCP use CIDR notation for ingress and egress rules, and visualizing the actual range prevents misconfiguration. For a practical walkthrough, see our guide on using CIDR and IP ranges in firewall rules. CIDR conversion is also useful for IP allowlisting, network audits, and capacity planning when allocating subnets within a larger address block.

Related Tools

Explore more free tools on My IP Help:

IP Range to CIDR — Convert a start and end IP address back into the smallest set of CIDR blocks.
Subnet Calculator — Calculate subnet details including network address, broadcast, and usable host range.

CIDR to IP Range Converter