Basic Sum symbols + Add Subtract / Divide * Multiply

Formulas can be very useful to enable a Content creator to (1) establish relationships between Family parameters and (2) to lock in a definite Parameter value.

E.g. 5 Panel window with Awning panel on each end and three centre panels that are equal in width.

Note: Usually once a formula has been entered the Parameter name becomes ghosted and is no longer directly editable in the Project file or from the value cell in the Type menu. (As shown above)

With formulas the following rules apply:

There should be a space between each parameter and the sum E.g. Parameter(space)+(space)Parameter = A + B

Parameter names are case and spelling sensitive. Match the parameter name exactly.

  • If you create a formula to lock a value of a Parameter, as shown above (Awning Panel Width = 900mm) then this value will be locked for ALL types within the family. This is a good idea for values that should be consistent across types. E.g. if you are creating a suite of windows and you want all suite frame depths to be 150mm.
  • Enclose separate sums with brackets. E.g. As seen above in Centre Panel Width = (Sum 1) / 3
  •  Instance Parameters cannot be included in formulas to determine the value of a parameter that is a Type parameter
  •  Revit Help menu has some more complex “IF”, “AND” and “Yes/No” formulas listed

© Copyright Reserved by Michelle Louw (Excerpt from My speaker notes at National Revit Technology Conference 2008.)