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Revit - Inconsistent Units and how to neutralize them.

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    Revit - Inconsistent Units and how to neutralize them.

    Inconsistent Units ! Probably THE error box in Revit that have caused me the most grief, over the years I´ve spent hours and hours on trying to work around it. But once I got the hang of it, and not least once I understood WHY Revit would throw that error box at me, it´s not that bad. Hope some of you will find this helpful.

    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 mm³>

    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>

    There´s probably a gazillion other possibilities, but I hope that this explains why we are getting the Inconsistent Units Error, and how to work around it.
    Klaus Munkholm
    "Do. Or do not. There is no try."

    I have caught Revit sometimes, when having to use items listed above, add the ' "foot" into a formula. This causes all types of greife. Look carefully its easy to miss.

    Thanks for the tips Klaus. Keep them coming.
    -Alex Cunningham


      Thanks, it really helped me!


        This post has been very helpful in my understanding of calculated values, thank you!
        But I am running into a problem while trying to create a workaround for my equipment schedule. We need to have a few existing Air Handlers in our schedule because we are only modifying part of them. What we need for the schedule is a "(E)" to show up in certian fields where we didn't change anything, for example, Supply Total Static Pressure.
        My idea was to create a conditional statment saying that when the STSP = 0, return "(E)", if false return STSP.
        if (Supply Total Static Pressure = 0, "(E)", Supply Total Static Pressure)

        I then thought it wasn't working because of two reasons: I was double-dipping with the same field in the same statement, and also the options of return for the true/false statement were in different units (text and Pressure) So I created another hidden field to try to convert the STSP from in-wg into a text field, then reference that field into my conditional statement. This is where I am stuck now getting "inconsistent units" with every variation I try. I only got it to work when I made the type "number", but then it wouldnt work in the 2nd calculated value.

        Attached are a couple screen shots of my calculated value attempts.

        Cond statement1 is my attempt at converting the pressure to text and says: Supply Total Static Pressure/1 in-wg
        Cond statement2 is my attempt at bringing in cond statement 1 into my conditional statement and says: if (Supply Total Static Pressure/1 in-wg = 0, "(E)", test1)

        Let me know if I'm completely wrong or kinda close here. There might be no way to put text and a number in the same statment, but I sure hope not.
        Thanks in advance for any help with this!

        Attached Files


          Unfortunately, Revit does not provide the users with functions to convert data types, as in other applications. At the moment, the available features don't allow us to take a value that is in other units and convert that into text, or concatenate that text to form something else.

          What is possible?

          If this length is this, this text is that.
          If this integer is this, this text is that.
          If this length or integer is this, this family type choice is that.

          What is not possible?

          If this text is this, this... [...any data type...] is that.
          Last edited by Alfredo Medina; November 21, 2012, 07:51 PM. Reason: format
          Freelance BIM Provider at Autodesk Services Marketplace | Linkedin


            Thanks Alfredo, I'll try to think of another route.


              I was wondering is it possible to write down a polynomial function in Formula field under Family Types, e.g. Pressure Drop, without getting Inconsistent Units Error?


                Originally posted by Dogma View Post
                I was wondering is it possible to write down a polynomial function in Formula field under Family Types, e.g. Pressure Drop, without getting Inconsistent Units Error?
                I've figure it out so I'll share.
                It is possible to write down a polynomial function. Just need to take care of measurement units. For instance:

                I'm creating a new family in Revit MEP (-> family types -> add new parameter -> pressure, velocity under mechanical and so on..)
                I would like to change the air velocity for my specific air terminal and get automatic result for pressure drop without looking up this specific item in the catalog.

                I've got the polynomial function in MS Excel (relation between velocity and pressure drop given by manufacturer).
                This is my equation:
                Δp = 2.7976 * v^2 + 1.0119 * v + 1.4286
                Typing this in Formula filed will give Inconsistent Units Error.

                So it needs to be written like this:
                2.7976 * v^2 * 1 s ^ 2 / 1 m^2 + 1.0119 * v * 1 s / 1 m + 1.4286

                This is how Revit process it:
                2.8 Pa *v ^ 2 * 1 s ^ 2 / 1 m² + 1.01 Pa * v * 1 s / 1000 mm + 1.43 Pa
                Last edited by Dogma; April 7, 2014, 11:12 AM.


                  I am looking to calculate the area of "DP1" by using cos(Roof Pitch)
                  "Roof Pitch" being an imported number that I chose.
                  Unfortunately i get the inconsistent units error.
                  I have made the roof pitch a slope parameter to make sure it is degrees but this doesn't seam to solve the problem.
                  Does anyone know how I might fix this.

                  I have tried writing it as - [1 Area] /cos([Roof Pitch])... makes no difference.

                  Attached Files


                    Your "1 Area" is not a distance measurement. Try using a length parameter for "1 Area"

                    Also you do not want to use the = character in your parameter names nor any other mathematical characters there are.
                    Last edited by Alex Cunningham; May 16, 2014, 05:51 AM.
                    -Alex Cunningham


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