Advanced Subnet Size Calculator

Size networks accurately with CIDR, masks, and ranges. Review capacity, wildcard masks, and usable hosts. Compare prefix options before assigning addresses across growing environments.

Subnet size calculator form

Enter any IPv4 address inside the subnet you want to analyze.
Examples: 24, 26, 27, or 30.
Use this to measure how many equal-size subnets fit inside a larger block.
Optional planning target for host capacity.
Optional target when subnetting a larger parent block.
Use this to hold back addresses for gateways, appliances, or future growth.

Plotly graph

This chart compares total addresses and usable hosts around the selected prefix.

Example data table

Network Subnet Mask Total Addresses Usable Hosts Usable Range Broadcast
192.168.10.0/24 255.255.255.0 256 254 192.168.10.1 - 192.168.10.254 192.168.10.255
172.16.20.128/26 255.255.255.192 64 62 172.16.20.129 - 172.16.20.190 172.16.20.191
10.12.8.0/27 255.255.255.224 32 30 10.12.8.1 - 10.12.8.30 10.12.8.31
10.50.4.240/28 255.255.255.240 16 14 10.50.4.241 - 10.50.4.254 10.50.4.255

Formula used

Total addresses
2^(32 - prefix)
Usable hosts
2^(32 - prefix) - 2 for most IPv4 subnets.
For /31, two addresses are usable on point-to-point links. For /32, one address exists.
Network address
IP address AND subnet mask
Broadcast address
Network address OR wildcard mask
Wildcard mask
255.255.255.255 - subnet mask
Equal-size subnets inside a base block
2^(child prefix - base prefix)

How to use this calculator

  1. Enter any IPv4 address that belongs to the subnet you want to inspect.
  2. Type the CIDR prefix, such as /24, /27, or /30.
  3. Optionally enter a base prefix to test subnetting inside a larger network.
  4. Add required hosts, required subnets, and reserved hosts for planning guidance.
  5. Click Calculate subnet size to show the result above the form.
  6. Use the CSV or PDF buttons to export the current results.

FAQs

1. What does subnet size mean?

Subnet size describes how many addresses exist inside a subnet and how many are usable for hosts. It is determined by the CIDR prefix or subnet mask.

2. Why are two addresses usually not usable?

Most IPv4 subnets reserve the first address as the network address and the last address as the broadcast address. Those two addresses are not assigned to normal hosts.

3. What is the difference between subnet mask and wildcard mask?

The subnet mask identifies network bits. The wildcard mask is its inverse and highlights host bits. Wildcard masks are commonly used in access control and routing rules.

4. Why does a /31 subnet show two usable addresses?

A /31 is commonly used on point-to-point links. Modern routing standards allow both addresses to be used, because broadcast traffic is not needed on that link type.

5. What is a base prefix used for?

A base prefix lets you test how many equal-size child subnets fit inside a larger parent network. It is useful during subnet planning and address allocation design.

6. Can this calculator help with subnet planning?

Yes. Enter required hosts, reserved hosts, and a desired subnet count. The calculator estimates a practical prefix and tells you whether the design is feasible.

7. Does this calculator support IPv6?

No. This version is designed for IPv4 subnet sizing. The formulas, range output, and binary display are all focused on 32-bit addresses.

8. Why does the result appear above the form?

The page is arranged to show the calculated values immediately below the header. That keeps the outcome visible first, while the form stays available underneath for fast edits.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.