Professional CIDR calculator for IPv4 subnetting. Calculate network range, broadcast addresses, and usable host capacity.
CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and IP routing. It replaced the older "Classful" network architecture (A, B, C) with a more efficient way to divide networks into smaller sub-networks (subnets) using a variable-length subnet mask.
The "/24" suffix indicates that the first 24 bits of the 32-bit IP address are used for the network identification, leaving 8 bits for host addresses within that network.
Designing a network—whether it is a small office LAN or a complex cloud VPC—requires a deep understanding of IP addressing. If you don't subnet correctly, you risk "IP Exhaustion" or overlapping network ranges that can crash your connectivity. Our IP Subnet Calculator is a vital tool for network engineers and system admins to plan IPv4 networks with precision using CIDR notation.
The -2 accounts for the mandatory Network and Broadcast addresses.
Every IP address is actually a 32-bit binary number. The Subnet Mask acts as a 'filter' that tells the computer which bits belong to the 'Network ID' (the building) and which bits belong to the 'Host ID' ( the individual room). For example, a /24 mask fixes the first 24 bits, leaving 8 bits for hosts (2^8 = 256). Understanding this binary math is the key to passing certifications like CCNA or Network+.
In the early days of the internet, IPs were divided into Class A, B, and C. This was extremely wasteful. CIDR (Classless Inter-Domain Routing) was introduced to allow for more flexible network sizes. With CIDR, you can create a network of exactly 512 IPs (/23) or just 4 IPs (/30). Our tool allows you to select any CIDR value and instantly see the resulting mask, usable range, and broadcast address.
Most internal networks use Private IP Addresses that are not routable on the public internet. The standard ranges are: 10.0.0.0/8 (Large), 172.16.0.0/12 (Medium), and 192.168.0.0/16 (Small). When designing a VPN or connecting two offices, you must ensure their private subnets don't overlap. Use our calculator to map out your available address space and prevent routing conflicts before they happen.
When you create a Virtual Private Cloud (VPC) in the cloud, you are asked for a CIDR block. AWS, for example, allows blocks between /16 and /28. If you choose a block that is too small, you won't be able to add more EC2 instances or Lambda functions later. If you choose one that is too large, it might conflict with your on-premise network. Using our Subnet Planner ensures your cloud infrastructure has enough 'headroom' for future growth.
Planning for a 200-device office.
Connecting two routers directly.
A subnet (subnetwork) is a logical subdivision of an IP network. It allows an organization to divide a large network into smaller, more manageable segments.
CIDR (Classless Inter-Domain Routing) uses a slash followed by a number (e.g., /24) to represent the number of fixed bits in the network mask.
A subnet mask is a 32-bit number used to differentiate the network portion of an IP address from the host portion.
A /24 network has a subnet mask of 255.255.255.0 and provides 256 IP addresses (254 of which are usable for hosts).
The first address is the Network Address and the last address is the Broadcast Address. Neither can be assigned to an individual host.
Public IPs are reachable over the internet. Private IPs (like 192.168.x.x) are used within a local network and are not directly accessible from outside.
A /30 has 4 total IPs, with only 2 usable hosts. This is commonly used for point-to-point links between two routers.
Used primarily in Cisco ACLs, a wildcard mask is the inverse of a subnet mask (e.g., /24 mask 255.255.255.0 has a wildcard of 0.0.0.255).
Class A (0-127), Class B (128-191), and Class C (192-223). Modern networking uses Classless (CIDR) routing instead of these rigid classes.
This tool is specifically for IPv4. IPv6 uses 128-bit addresses and different subnetting rules (usually /64 for LANs).