What is CIDR notation and how does this calculator use it?
CIDR stands for Classless Inter-Domain Routing. It’s the standard method for representing IP addresses and their associated network prefix in a compact format. A CIDR address looks like this: 192.168.1.0/24 — the number after the slash tells you how many bits belong to the network portion of the address.
This subnet and CIDR calculator uses that prefix number directly. Select any prefix from /8 to /32 in the dropdown, enter your IP address, and the calculator instantly computes everything derived from that CIDR notation — the network address, broadcast address, subnet mask, wildcard mask, usable host range, and a full binary breakdown showing exactly which bits are network bits and which are host bits.
CIDR replaced the old Class A, B, C system in 1993 because classful addressing wasted enormous amounts of IP space. A company that needed 300 hosts had to take an entire Class B network with 65,534 addresses, wasting over 65,000 IPs. CIDR allows networks to be sized precisely to their needs — a /23 gives exactly 510 hosts, a /22 gives 1,022, and so on.
Common CIDR prefixes and what they mean:
A /32 is a single host — one specific IP address. A /30 gives 2 usable hosts and is used for point-to-point links between routers. A /29 gives 6 usable hosts. A /28 gives 14. A /27 gives 30. A /26 gives 62. A /25 gives 126. A /24 — the most common — gives 254 usable hosts and is a single standard subnet. A /23 gives 510 hosts across two Class C ranges. A /22 gives 1,022 hosts. A /16 gives 65,534 hosts. A /8 gives over 16 million.
Use the CIDR cheatsheet tab in the calculator above to see all common prefixes with their host counts at a glance.
What is a CIDR calculator? A CIDR calculator takes an IP address written in CIDR notation — like 192.168.1.0/24 — and computes the network address, broadcast address, subnet mask, wildcard mask, and usable host range. This free tool does all of that instantly in your browser with no signup required.
What does /24 mean in CIDR notation? The /24 means the first 24 bits of the IP address identify the network, leaving 8 bits for host addresses. In practical terms a /24 gives you 254 usable host addresses — from .1 to .254 — with .0 reserved as the network address and .255 reserved as the broadcast address.
What is the difference between a subnet mask and CIDR notation? They represent the same information in different formats. A /24 CIDR prefix is identical to a 255.255.255.0 subnet mask. CIDR notation is shorter and more convenient to write. This calculator shows you both — enter your CIDR prefix and it displays the equivalent subnet mask automatically.
What does CIDR stand for? CIDR stands for Classless Inter-Domain Routing. It was introduced in 1993 to replace the older Class A, B, C addressing system and allow more flexible allocation of IP address space. Today CIDR is the universal standard for IP addressing on the internet.
How do I calculate a CIDR network address? Enter your IP address and CIDR prefix into the calculator above and click Calculate. The network address is automatically computed by applying the subnet mask to your IP address using a bitwise AND operation. The binary breakdown tab shows exactly how this works bit by bit.
What is a subnet calculator? A subnet calculator takes an IPv4 address and CIDR prefix length and instantly computes the network address, broadcast address, subnet mask, usable host range, and total number of hosts. It saves network engineers and students from doing manual binary math.
What is CIDR notation? CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated network prefix. For example, 192.168.1.0/24 means the first 24 bits define the network, leaving 8 bits for hosts — giving you 254 usable addresses.
How do I use this calculator? Enter your IPv4 address one octet at a time, select your prefix length from the dropdown, and click Calculate. The results appear instantly — no page reload needed.
How many hosts does a /24 subnet support? A /24 subnet supports 254 usable hosts (256 total addresses minus the network and broadcast addresses).
What’s the difference between a subnet mask and a wildcard mask? A subnet mask uses 1s to identify network bits. A wildcard mask is its inverse — used in access control lists and routing configs to define which bits to ignore.
What is a broadcast address? The broadcast address is the last address in a subnet. Packets sent to it are delivered to every device on that network.
Can I use this for IPv6? This calculator is designed for IPv4. IPv6 uses 128-bit addresses and requires a separate tool.