Subnet & CIDR Calculator
Calculate network address, broadcast address, and usable hosts instantly.
| Network Address | -- |
|---|---|
| Broadcast Address | -- |
| Usable Host Range | -- |
| Total Usable Hosts | -- |
| Subnet Mask | -- |
| CIDR Notation | -- |
| Wildcard Mask | -- |
| IP Class | -- |
Understanding Subnetting & CIDR
What is CIDR Notation?
CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing. Instead of relying on rigid A, B, and C classes, CIDR uses a suffix like /24 which indicates the number of bits used for the network portion of the address (e.g., 24 bits out of 32 total).
Network vs Broadcast Address
- Network Address: The first address in the subnet. It represents the network itself and cannot be assigned to a host.
- Broadcast Address: The last address in the subnet. It is used to send data to all hosts on the network.
- Usable Hosts: Every address between the Network and Broadcast addresses. (Calculated as
2^(32 - CIDR) - 2).
What is Subnetting?
Subnetting is the practice of dividing a single large network into multiple smaller, more manageable sub-networks (subnets). This improves network performance by reducing broadcast traffic and enhances security by isolating different departments or server groups.
This calculator uses 100% offline mathematical bitwise operations to instantly compute the network boundaries based on the IP address and Subnet Mask (or CIDR notation) you provide.
Understanding the Output
The very first IP address in the subnet. It acts as the identifier for the network itself and cannot be assigned to a computer or device.
The very last IP address in the subnet. Data sent to this address is received by every single device on that specific subnet. It cannot be assigned to a device.
The block of IP addresses situated strictly between the Network Address and the Broadcast Address. These are the IP addresses you can actually assign to servers, laptops, phones, and routers.
What is CIDR Notation?
CIDR (Classless Inter-Domain Routing) notation is a compact way to represent an IP address and its associated routing prefix (subnet mask). Instead of writing out a long mask like 255.255.255.0, you can simply write /24.
The number after the slash represents how many bits in the 32-bit IPv4 address are locked for the network prefix. For example, in a /24 network, 24 bits are used for the network, leaving 8 bits (32 - 24) available for host addresses (resulting in 256 total addresses, or 254 usable hosts).
| CIDR | Subnet Mask | Usable Hosts | Common Use |
|---|---|---|---|
| /24 | 255.255.255.0 | 254 | Standard home/small office network |
| /23 | 255.255.254.0 | 510 | Medium office |
| /16 | 255.255.0.0 | 65,534 | Large corporate network |
| /30 | 255.255.255.252 | 2 | Point-to-point router links |
Frequently Asked Questions
What does CIDR notation like /24 actually mean?
The number after the slash indicates how many bits of the 32-bit IPv4 address are fixed as the network portion — /24 means the first 24 bits identify the network, leaving 8 bits (256 addresses, 254 usable) for hosts.
Why is the number of usable hosts always 2 less than the total addresses in a subnet?
Every subnet reserves its first address as the network address and its last address as the broadcast address — neither can be assigned to an individual host, which is why a /24 subnet has 256 total addresses but only 254 usable ones.
What's the difference between a subnet mask and CIDR notation?
They express the same information differently — a subnet mask like 255.255.255.0 spells out which bits are network bits in dotted-decimal form, while CIDR notation (/24) states the same thing as a bit count. They're mathematically interchangeable.
Why would I subnet a network instead of using one large block?
Subnetting divides a large address block into smaller, isolated segments — improving security (limiting broadcast domains), organizing departments or services, and using IP address space more efficiently instead of wasting a huge block on a small number of devices.
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