Last week I covered how to quickly put together a ControlLogix system BOM using IAB.

Today I'll walk you through two ways you can use the same software to to insure your design does not exceed the capacity of the controller you've selected.

In the above image you can see a ControlLogix system I build for a lesson I was teaching students of my Logix Live™ online course. Specifically, the image shows the process of adding the controller to a network.

I then go on to add some distributed I/O, VFDs, and HMIs to my example system in much of the same way:

Once your devices have been added to your network, you can view the entire system network by selecting the “network” tab at the bottom of the application:

Here's what my example system looked like when I've finished – it includes five racks of Flex5000 IO, six PowerFlex VFDs, and three HMIs:

Now that I've added all my devices, I'm ready to open the “Advanced Communication Details” under the “Action” menu:

Once open, I first need to add the expected number of tags each of my HMIs will have. Below you can see I selected 500 Standard Tags, and 1 String Tag for each HMI:

With those values entered,  I click over to the results tab where in the below image you can see I've used 11 of 89 Ethernet/IP Nodes, .6 or 2.4mb of memory, and roughly 2% of both the Comms and HMI Utilization:

Now for those who need a quicker estimate without having to select all the components in your system, there's a second way to estimate the capacity of a ControlLogix controller on Ethernet/IP.

To access it, save your work and create a new Workspace in IAB, but this time choose “Ethernet/IP Capacity Subsystem” as shown below:

Once the capacity window opens, select your controller from the top middle of the window as shown below:

Next, we'll start on the top left of the window and click on “Select I/O,” and in the popup we'll add the same 5 chassis of Flex5000 I/O with 6 digital and 2 analog modules and then click on “OK”:

Now we'll move over one spot to the right and click on “Select I/O” again and add 6 PowerFlex 525 drives:

And in the third location we'll add 4 PanelView Plus terminals with 500 standard tags and 1 String Tag:

With all our devices added, the final step is to click on the “Compute” on the left middle of the window to get the below results:

In the results above you can see I've used 11 Ethernet Nodes, 2.1% of the I/O utilization, and 2.8% on the HMI utilization (I added an extra HMI in this second example.)

Now that I've shown you how to calculate a ControlLogix System's capacity, why not learn how to setup, program, and troubleshoot Rockwell's ControlLogix using RSLogix 5000 or Studio 5000 by taking my ControlLogix course, PAC Basics?

For a limited time, anyone who enrolls in PAC Basics Extended Edition will also get a free copy of my next course, ULTIMATE Logix Course™ as well as a lifetime copy of every YouTube video I've ever published on the ControlLogix Programmable Controller.

If you have any questions about those courses, please don't hesitate to contact me here.

And if you have other questions, I invite you to sign-up for my new community at

Until next time my friends, Peace!


Shawn Tierney
Automation Instructor and Blogger

Have a question or comment on this article? Join our community to take part in the discussion! You'll also find all of my courses at