How to Calculate a Subnet Range Step by Step

To calculate a subnet range, you need an IPv4 address and either a CIDR prefix (such as /24) or a subnet mask (such as 255.255.255.0).

Once you know the subnet boundary, you can determine the network address, broadcast address, and usable host range.

• Network address
• Broadcast address
• First usable host
• Last usable host
• Total number of addresses
• Number of usable hosts

The process for calculating a subnet range follows a consistent pattern:

• Identify the subnet size (CIDR or mask)
• Determine the block size
• Find the network boundary
• Calculate the broadcast address
• Determine usable host range

Given the IP address 192.168.1.50/24:

CIDR: /24
Subnet mask: 255.255.255.0

Network:   192.168.1.0
Broadcast: 192.168.1.255

Usable:    192.168.1.1 - 192.168.1.254

Total IPs: 256
Usable IPs: 254

A /24 means the last octet is used for hosts, giving a block size of 256 addresses.

Now consider a smaller subnet: 192.168.1.50/27

CIDR: /27
Subnet mask: 255.255.255.224

Block size: 32

Network:   192.168.1.32
Broadcast: 192.168.1.63

Usable:    192.168.1.33 - 192.168.1.62

Total IPs: 32
Usable IPs: 30

The key step is identifying the block size and finding which range the IP falls into.

Block size is calculated by subtracting the subnet mask value from 256 in the relevant octet.

Mask: 255.255.255.224

256 - 224 = 32

Block size = 32

When working in the last octet, list the block boundaries and find where the IP fits. For a /27, the ranges begin at 0, 32, 64, 96, 128, 160, 192, and 224. An address like 192.168.1.50 falls into the 32 to 63 block, so 192.168.1.32 is the network and 192.168.1.63 is the broadcast.

That shortcut saves time because you do not need to recalculate everything from scratch for every address. You just need the mask, the block size, and the correct boundary.

• Forgetting to exclude network and broadcast addresses in traditional IPv4 subnets
• Using the wrong octet when calculating block size
• Assuming all subnets are /24
• Mixing CIDR and subnet mask incorrectly
• Applying the usual host-range rule to /31 or /32 without checking the intended design

Most everyday subnet calculations assume a network address, a broadcast address, and a remaining usable host range. That model works well for common IPv4 LAN sizes such as /24, /27, or /30.

Very small prefixes such as /31 and /32 are special cases, so treat them separately instead of forcing them into the normal subtract-two mental shortcut.

Subnet calculations are used in VLAN design, firewall rules, routing decisions, and cloud networking.

Being able to quickly calculate ranges is a core networking skill for troubleshooting and planning.

Instead of calculating manually, you can use the DNS Pro Subnet Calculator to generate subnet ranges instantly.

You can enter an IP with CIDR, or an IP with subnet mask, and get the full range immediately.

• What Is a Subnet Mask?
• What Is CIDR Notation?

If you want to validate this topic in practice, these DNS Pro tools are the fastest next step.

• Subnet Calculator
• CIDR Converter
• Private vs Public IP Checker