USING FORMULAS IN FAMILIES

TEXT

You can't pass the value of a text parameter to another text parameter.

e.g.

Fire Rating = FireRating

It works when editing the family, but if the parameter is changed in the project it won't change the other parameter.

You can not use text parameters in an evaluation formula (e.g. in an IF statement).

e.g:

if(TextParameter="Yes", "Ahuh", "Nah")

But results can be put into a text parameter:

if(NumberParameter = 1, , "Ahuh", "Nah")

Which means you also can't test for null or empty text strings.

NUMBERS

The basic operators (add, subtract, multiply, ect.) have been left out on purpose, but feel free to add more useful formulas, that you use in your families.

The valid formula abbreviations for arithmetic operations and trigonometric functions in Revit are:

• Addition: +

• Subtraction: -

• Multiplication: *

• Division: /

• Exponentiation: ^

• x^y, x raised to the power of y

• Logarithm: log

• Square root: sqrt

• sqrt(16)

• Sine: sin

• Cosine: cos

• Tangent: tan

• Arcsine: asin

• Arccosine: acos

• Arctangent: atan

• 10 raised to an x power: exp(x)

• Absolute Value: abs

• Pi: pi (3.1415926...)

• round: round to nearest

• roundup: round up

• rounddown: round down

Exponentiation

X raised to the power of Y = X ^ Y

E raised to an x power

E is a mathematical constant that is approximately equal to 2.7. It is an irrational number, but if we truncate it to 20 decimals it would be 2.7182818284590452353.

Revit usage = exp(x)

Circles with pi p

Usage in Revit = pi()

Circumference = pi() * (Radius * 2)

Circumference = pi() * Diameter

Circle Area = pi() * Radius ^ 2

Square Root

Fixed value = sqrt(999)

Parameter = sqrt(Width)

Formula= sqrt(Width + Height)

Logarithm

The logarithm of a number to a given base is the exponent to which the base must be raised in order to produce that number. For example, the logarithm of 1000 to base 10 is 3, because three factors of 10 must be multiplied to yield a thousand: 10?×?10?×?10 equals 1000

Revit usage = log(1000)

Round Function In Formulas

Values in formulas can be now rounded up or down. For example, when riser height is calculated, one needs the function “round” to find the appropriate value.

ROUND(x)

The round function returns a number (NOT a length) rounded nearest to a whole number. It doesn’t take into consideration rounding direction (round up or down). If the number is (for example) from 24.5 to 24.9, the function rounds it to 25. If it is from 23.1 to 23.4, the function rounds it to 23.

Examples:

round ( 23.4) = 23

Round ( 23.5) = 24

Round ( 23.6) = 24

Round (-23.4) = -23

Round (-23.5) = -23

Round (-23.6) = -24

Syntax

The syntax for the round function is: round( number)

number is the number to round.

ROUNDUP(x)

“x” is a unitless value that should return the largest integral value less than or equal to x.

For example:

roundup ( 23.0) = 23

roundup ( 23.5) = 23

roundup ( 23.9) = 23

roundup (-23.0) = -23

roundup (-23.5) = -24

roundup (-23.9) = -24

The syntax for the roundup function is: roundup (number)

number is the number to round up.

ROUNDDOWN(x)

“x” is a unitless value that should return the smallest integral value greater than or equal to x.

For example:

rounddown ( 23.0) = 23

rounddown ( 23.5) = 24

rounddown ( 23.9) = 24

rounddown (-23.0) = -23

rounddown (-23.5) = -23

rounddown (-23.9) = -23

The syntax for the rounddown function is: rounddown (number)

number is the number to round down.

Note that when numbers such as 23.5 are rounded, they can result in either 23 or 24. To produce a stable result, for all the .5 cases, we round to the larger integer. That means that 23.5 is rounded to 24, while -23.5 to -23

Force yes/no parameters to be checked or unchecked

Force checked = 1 < 2

Force unchecked = 1 > 2

Conditional statements

Conditional statement uses this structure:

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

Supported Conditional Operators

< Less than

> Greater than

= Equal

/ Divide

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)

Simple IF Statement

IF (Length < 900, <true>, <false>)

Formula That Returns Strings

IF (Length < 900, “Opening too narrow”, “Opening OK”)

Using logical AND

IF ( AND (x = 1 , y = 2), <true>, <false>)

Returns <true> if both x=1 and y=2, else <false>

Using logical OR

IF ( OR ( x = 1 , y = 2 ) , <true>, <false>)

Returns <true> if either x=1 or y=2, else <false>

Nested IF statements

IF ( Length < 500 , 100 , IF ( Length < 750 , 200 , IF ( Length < 1000 , 300 , 400 ) ) )

Returns 100 if Length<500, 200 if Length<750, 300 if Length<1000 and 400 if Length>1000

IF with Yes/No condition

Length > 40

Returns checked box (<true>) if Lenght > 40

NOT with Yes/No condition

not(Viz)

Returns checked box (<true>) if Yes/No parameter "Viz" is unchecked, and returns unchecked box (<false>) if Yes/No parameter "Viz" is checked.

IF AND OR Returning the greatest of three values

Say you have these 3 length parameters, and want a fourth parameter to return the greates value/lenght of the 3:

Length A

Length B

Length C

Return Length (Returns the greatest of the three length parameters)

Return Length = if(and(or(Length A > Length B, Length A = Length B), or(Length A > Length C, Length A = Length C)), Length A, if(and(or(Length B > Length A, Length B = Length A), or(Length B > Length C, Length B = Length C)), Length B, if(and(or(Length C > Length A, Length C = Length A), or(Length C > Length B, Length C = Length B)), Length C, 0 mm)))

Credit to: Joe Zhou for this formula!

Another option is to use an extra "Calc" parameter, which is a bit more clumsy but also way easier and more manageable for us mortals.

Calc = if(Length A > Length B, Length A, Length B)

Return Length = if(Calc > Length C, Calc, Length C)

And a third option:

Return Length = if(A > D, if(A > C, if(A > B, A, B), if(B > C, B, C)), if(B > D, if(B > C, B, C), if(C > D, C, D)))

Trigonometry for right triangles:

Known: a+b

c = sqrt(a ^ 2 + b ^ 2)

A = atan(a / b)

B = atan(b / a)

Known: a+c

b = sqrt(c ^ 2 - a ^ 2)

A = asin(a / c)

B = acos(a / c)

Known: b+c

a = sqrt(c ^ 2 - b ^ 2)

A = acos(b / c)

B = asin(b / c)

Known: c + A

a = c * sin(A)

b = c * cos(A)

B = 90° - A

Known: c + B

a = c * cos(B)

b = c * sin(B)

A = 90° - B

Known: a + B

b = a * tan(B)

c = a / cos(B)

A = 90° - B

Known: b + A

a = b * tan(A)

c = b / cos(A)

B = 90° - A

Known: a + A

b = a / tan(A)

c = a / sin(A)

B = 90° - A

Known: b + B

a = b / tan(B)

c = b / sin(B)

A = 90° - B

Range of Values

Given the following parameters:

user_value:

min_value:

max_value:

actual_value: = if (user_value < min_value, min_value, if (user_value > max_value, max_value, user_value))

Specify a range of valid entries, with the min_value and max_value parameters; then, use the actual value if it is within the range; otherwise, use your minimum or maximum values.

Circular Segments.

Here's how to calculate the Segment length, the Chord Length, the Angle etc. (Image should speak for itself)

DATE CALCULATIONS

Julian Day is the continuous count of days since the beginning of the Julian Period used primarily by astronomers.

A count for each Date means I can subtract one from other to find the days in between.

I also didn't want to have 6 entry parameters(y/m/d) for two dates so I've made 2 integer parameters which I parse into y/m/d and correct with DRV(drive) parameters and concatenate back into check parameters.

DateA (Integer Parameter)

year(at least 1 digit)month(2 digits)day(2 digits). So the earliest date you can enter is 10101.

Parsing done by getting the correct decimal places.

AyearParse = rounddown(DateA / 10000)

AmonthParse = rounddown(DateA / 100) - (AyearParse * 100)

AdayParse = DateA - (AyearParse * 10000) - (AmonthParse * 100)

I've used the same day / month / yearDRV(drive) parameters from the Revit Calendar.

Julian Day Number

You must compute first the number of years (y) and months (m) since March 1 −4800 (March 1, 4801 BC):

So be it!

Aa = rounddown((14 - AmonthDRV) / 12)

Ay = AyearDRV + 4800 - Aa

Am = AmonthDRV + (12 * Aa) - 3

Let´s begin with some basic algebra:

<100 mm * 100 mm = 10,000 mm²>

So if you have a Length parameter, and try to use a (Length * Length) formula, you´ll get the " Inconsistent Units" error, because (Length * Length = Length Squared). Only way around is to neutralize the units on at least one of the parameters in the formula. The easiest way to neutralize a unit is by dividing by 1 (one):

<100 mm * (100 mm / 1 mm) = 10,000 mm>

Why? Because <100 mm / 1 mm = 100> (unit less) and <100 mm * 100 = 10,000 mm>

And another example:

<100 mm * 100 mm * 100 mm = 1,000,000 mm>³>

So again, if you need to multiply 3 length units in a Area or Length parameter, you´ll need to neutralize the units as above.

<100 mm * 100 mm * (100 mm / 1) = 1,000,000 mm²>

<100 mm * (100 mm / 1) * (100 mm / 1) = 1,000,000 mm>

So far, dividing by 1 (one) have been a success, but in some cases it´s necessary to multiply by 1 (one) instead. An example: You want to multiply two Number parameters into a Length parameter:

<100.0 * (100.0 * 1) = 10,000 mm>

Another common situation for the "Inconsistent Units" error, is when quantifying costs in schedules

In the schedule you already have "Area" and "Cost" but want to add a Calculated Value "Total Cost":

<Area * Cost = Inconsistent Units>

<(Area / 1) * Cost = Total Cost>