To satisfy your inner API maths hunger (surely that’s a thing?), here is how Revit “thinks” about Length:

Notice the recurring “328083…” theme? This is how it relates:

Check out the comprehensive list of Revit internal units (across all unit types) at:
Revit Units .NET API: Figure Out Revit Internal Units Per Unit Type (pt. 2) – RevitNetAddinWizard & NavisworksNetAddinWizard

Paolo has “managed to complete tools for conversion from internal units and metric (meters, centimeters and millimeters) for lengths, areas and volumes (LAV).”

Download these and put them in C:AutodeskDynamoCoredefinitions

Original post:

We know that each Revit project has a Unit setting (Manage – Project Units).  This dictates the default entry units (while typing the Length of a wall, for example.)

However, what if you want to enter a different type of unit without changing the Project Units all the time?

Revit natively understands a number of different unit types, and it will transparently convert them into the appropriate Project Units for you.  All you have to do is type xxx SUFFIX, where xxx is the unit you want to convert, and SUFFIX is the type of unit it is.

Here is a list of the natively supported units of Length (that I know of):


      Note – you can also use 2 apostrophes (foot marks) for inches –(via @DBCdoug on Twitter)

How do you insert feet? Use the apostrophe (next to Enter key):

What about a combined feet-and-inches unit?  Yes, you can!  You can use a dash to divide the two (but you don’t have to).  Here are some possible combinations that work:

These can all be entered WITH or WITHOUT a space.  For example:
12 cm

Interestingly, the ft suffix does not work for feet UNLESS you have it combined with inches, at least on Revit 2011 / 2012.  For instance:
2ft-0in DOES WORK

Crazy!  Even:

Where in Revit can you use these inbuilt conversions?  You will most likely use them in direct entry locations (while drawing a wall, for instance), or in the Options Bar:

Direct entry

Options Bar

If you have any other tips on Unit entry, feel free to comment.