Switching Units From MM to Mils and Other PCB Design Measurement Preferences

Created: August 3, 2018
Updated: December 16, 2020
Image of rulers with both units switching from MM to mil

There was a time when the unit of measurement that a PCB designer utilized was dependent on the side of the world they were currently residing in. Gradually, that began to change as the metric system became the standard unit of measurement. The problem, however, was that many older data sheets and designs still referenced imperial measurements. Designers had to arm themselves with a scratch pad, calculator, and a bottle of aspirin to constantly calculate the conversions between the two.

To our immense relief, CAD programs began to incorporate the ability to switch between units of measurement in their software, thereby eliminating the need for manual conversions. Altium Designer is an excellent example of a PCB design system that allows the user to easily switch from MM to Mils or Mils to MM. This kind of flexibility, along with a host of other system settings and preferences, can save you lots of time and headaches when it comes to working on your PCB designs. Let’s take a quick look at how seamlessly switching between PCB measurement units can save you time.

Switching from MM to Mils in the Schematic

When you first open up Altium Designer, before you even move to the snap grid, you can set up some preferences for working in the schematic. These preferences can be found by clicking on the gear wheel in the upper right corner of the Altium Designer as shown below. You can also access these preferences with a schematic sheet open by going to the “Tools” pulldown menu and selecting “Preferences.”

Opening the Preferences dialog in Altium Designer

The preferences dialog box gives you the ability to set up how you want the different tools in Altium Designer to behave when you first open them. In the schematic, you can set up behaviors for just about everything from sheet templates to how it is going to zoom into PCB library components. There are also different settings for PCB measurement units as you can see below.

Three different areas where you can set the units in Altium Design’s schematic preferences

In the picture above, you can see three different areas where you can set unit preferences for a new schematic in Altium Designer. The first is the main units for the schematic, which is found in the “General” settings of the preference dialog. The second allows you to set unit preferences for grids, while the third is for setting the units of your default primitive objects.

You are not restricted to the PCB measurement units that were set up in the preferences when working in a schematic, however. You can easily change units on the fly as you work by using the “Toggle Units” command in the “View” pulldown menu. Look closely at the picture below, and you can see that command in the pulldown menu. Notice that the “U” in “Units” is underlined. This means that you can use this letter in a keystroke combination to toggle the units as well. In this case, the command is in the “View” pulldown, so you would need to use the keystroke combination of “vu” to change the units.

The Toggle Units command in the View pulldown menu

Switching from MM to Mils in Layout

On the PCB layout side of Altium Designer, things a little different. In previous versions of the PCB editor in Altium Designer, the units were changed in the “Board Options” menu. This has now moved to the properties panel, which can be accessed from the “Panels” button. Another thing that we should mention is that instead of “Metric” and “Imperial,” Altium Designer now refers to units of measurement as “MM” (Millimeters) or “Mils” units.

If you’re looking to change your PCB editor measurements, if you need to demonstrate components or traces as imperial units, then you’ll need to locate your board options. To change the units of measurement for the board, open up the “Properties” panel, and scroll down to the bottom. There you can find the units in the “Other” section of the Properties panel, as shown in the picture below.

The units switch in the properties panel of Altium Designer’s layout tool

When you change the units, the location and grid data displayed in the lower-left corner of the session window will update. Take a look at the picture below, and you can see the difference in data when we toggle from one unit of measurement to the other. This display of data is also found in the same location in the schematic editor as well.

The display of PCB measurement units in use in Altium Designer

There are some other ways to change the units of measurement in Altium Designer’s layout tool. You can use the command: “Toggle Units” found in the View pulldown menu as shown below. As with the schematic, you can also use the keystroke shortcut combination of “vu” to change the units. You also have one other option in layout to change the units, and that is to use the keystroke shortcut of “q.”

The View > Toggle Units command in Altium Designer’s layout tool

There are other locations in Altium Designer where you can make changes to the units of measurement as well. For instance, the layer stack manager gives you the ability to toggle the units being used to develop the stackup.

Simplified Controls to Make You More Productive

In addition to the units that you are working in, Altium Designer gives you many other simplified controls to change your working environment. You have an incredible amount of control over the snap grids that you use, both in setting them up and in switching between them. In layout, you can control the display of your layers and switch between them by using the View Configuration panel which is easily accessed with the keystroke shortcut of a lower case “L.” Do you want to switch between 2D and 3D, use the “View” pulldown menu as shown below or simply use the keystroke shortcuts of “2” or “3.”

You can easily switch between the 2D and the 3D view in Altium Designer

No matter what we are doing in Altium Designer, we have found that it has been configured to work with us to make our job easier. The ease of toggling back and forth between PCB measurement units is just one example of this. If you are new to Altium Designer, we hope that this has helped you to get a running start on using it. If you haven’t used it yet, take a look at what it has to offer. You will discover that Altium Designer is one of the most productive and powerful sets of PCB design tools out there.

PCB design software, like Altium Designer, has many easy-to-use features that make you faster and more productive in your work. If you would like to learn more about how Altium can help you with your next printed circuit board design, talk to an expert at Altium.

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