Default Units and Units Display

Default Units and Units Display

Settings for 3D Documents/Workspaces

Fusion 360 can work In a variety of different units and even mixed units.

To change units in a open document:

  • Go to the browser and scroll to the top.
  • Hover over the "Units: mm" browser node. An edit icon will appear at the end of the node. Click this icon to edit the units.
  • A command dialog opens and allows you to change units. You can select from mm, m, in or feet.

Note that sketch dimensions will show in the active units. If you edit these sketch dimensions they will remember what units were entered.

If you prefer to set your units for all new documents you can change this.

  • Open the application Preferences from the upper right menu where you see your login name.
  • Along the left side navigation go to the Default Units categories.
  • Set the default units you would like for future new designs.

You can also set units for CAM and Simulation studies. Simulation unit preferences allow setting any of the default units used when setting up a simulation study so there are significantly more options available.

While we are looking at application preferences and units, there is another group called Unit and Value Display. This allows control over how units are displayed.

Several options are useful to look at and several need a little explaining on what they do.

First, Let's review a few settings I like to change.

  • General Precision for mm is fine at 2 decimal places. The default is 3.
  • Scientific notion default setting kicks in way to early. I prefer to be able to get at 6 significant digits when I'm doing precision measuring. So I set the scientific notion to show 7 digits.
  • This also means setting notation to display at 0.0000001 and below. I don't bother setting the above value as I have never measured anything large enough to need to.

A pair of settings that can trip people up have to do with Trailing zeros. First, these settings do not affect drawings. We will look at that next. These settings only have to do with 3D workspaces/documents. You can turn on or off the display of trailing zeros by enabling the check-box option. Lets leave the default ON. Since we are working in 2 decimal place precision it is nice to always show two places and the Minimum precision setting allows you to set how many places are always displayed even if hide trailing zeros in on. This is easier to explain with examples. Given the options set as described the following values will be displayed as such:

1.123000 = 1.12 ( 3 rounds down )
1.456000 = 1.46 ( 6 rounds up )
1.005000 = 1.01 ( 5 rounds up )
1.100000 = 1.10 ( Minimum show 2 places even if zeros )

While you never actually should see this its worth knowing that Fusion 360's internal units is centimeters (cm). All units in the database are stored as cm and each client's units display settings simply affects the conversion/display of these internal values. This means you can swap units anytime an you can mix and match designs of different unit systems and everything will be accurately sized. Autodesk Shape Manager, Fusion 360's geometry kernel, is accurate to at least 6 significant digits. Therefore 0.000001 cm is an accuracy of .01 microns or .01 µm. If you try and do solid modeling operations below this size you may get modeling failures.

Occasionally you may work with 3D file formats that do not define the data's units. After inserting uploading these for translation and reuse in your projects, you may need to scale the data up or down. Depending on the source applications internal units you may need to use a factor of 2.54 ( in to cm conversion )or 10 ( mm to cm ). While this is inconvenient the lack of declared units in these 3D files makes this unavoidable.

Settings for 2D Documents/Workspaces

The set default Units for drawings we return to the General section on preferences and choose Drawings.

The first option for Standard defaults to Inherit from design. This is not obvious what it does sine 3D designs don't have standards (yet). The standard is somewhat questionable determined by default units.

  • in or ft = ASME
  • mm, cm or m = ISO

I always use ASME title blocks and borders. So I change the first setting to always be ASME. We can leave the Annotation Units to Inherit since this will set the drawing to match in, ft or mm as set by the 3D design.

Hopefully these few options will unlock some of the secrets of units and their default display in your designs.