Revit Families 103 – Formula Basics

A conditional statement uses this structure:

IF (<condition>, <result-if-true>, <result-if-false>)

This means that the values entered for the parameter depend on whether the condition is satisfied (true) or not satisfied (false). If the condition is true, the software returns the true value. If the condition is false, it returns the false value.

Supported Conditional Operators

<	Less Than
>	Greater Than
=	Equal to
/	Divide: Length / 8
AND	Both statements are true
OR	One of the statements is true
NOT	Statement is false

Conditional statements can contain numeric values, numeric parameter names, and Yes/No parameters.

Currently, <= and >= are not implemented. To express such a comparison, you can use a logical NOT. For example, a<=b can be entered as NOT(a>b). For more information see “Revit Families 402 – Greater Than or Equal To“

Sample Conditional Statements

Simple IF Statement
IF (Length < 30′, 2′ 6″, 4′)

Formula That Returns Strings
IF (Length > 30′, “This thing is tall”, “This thing is short”)

Using logical AND
IF ( AND (x = 1 , y = 2), 8 , 3 )

This will return <true> if both x=1 and y=2, else <false>

Using logical OR
IF ( OR ( A = 1 , B = 3 ) , 8 , 3 )

This will return <true> if either A=1 or B=3, else <false>

Nested IF statements
IF ( Length < 10′ , 1′ , IF ( Length < 20′ , 2′ , IF ( Length < 30′ , 3′ , 4′ ) ) )

Returns 1′-0″ if Length<10′-0″, 2′-0″ if Length<20′-0″, 3′-0″ if Length<30′-0″ and 4′-0″ if Length>30′-0″

IF with Yes/No condition
Length > 10
(Note that both the condition and the results are implied.)

Returns checked box <true> if Length > 10

NOT with Yes/No condition
not(myCheckbox)

Returns checked box (<true>) of Yes/No parameter “myCheckbox” is unchecked, and it returns <false> if “myCheckbox” is checked.

Rounding

Prior to Revit 2012 the only way to round numbers was to pass a number through an integer parameter. The integer parameter always rounds to the nearest whole number with the standard mathematical rounding rules of:

Down -> for fractions of 0.0 to 0.49 and -0.5 to -0.99
Up -> for fractions of 0.05 to 0.99 and -0.49 to 0.0

As of Revit 2012 we now have three additional functions to use!!

Note that “x” is unit-less

Round(x)
Rounds to the nearest whole number per the standard rules mentioned above.

round (1.1) = 1
round (1.5) = 2
round (1.7) = 2

round (-1.1) = 1
round (-1.5) = 1
round (-1.7) = 2

Roundup(x)
Rounds to the largest whole number greater than or equal to “x”.

round (1.0) = 1
round (1.5) = 2
round (1.6) = 2

round (-1.0) = 1
round (-1.5) = 1
round (-1.6) = 1

Rounddown(x)
Rounds to the smallest whole number less than or equal to “x”.

round (1.0) = 1
round (1.5) = 1
round (1.6) = 1

round (-1.0) = 1
round (-1.5) = 2
round (-1.6) = 2