topic Re: Dimension rounding error in Revit Architecture Forum

Dimension rounding error

jbrr27 — Wed, 09 Mar 2022 03:04:14 GMT

I have some elevations that are being submitted to the city where we have to show variations in our facade at a proscribed distance. To show compliance, I created a dimension type with 1" tolerance (exact measurements aren't critical, and I don't want fractional dimensions cluttering up the views). I have several equally spaced bays, and the exact measurement is 37'-9 1/2". On my elevation with the 1" tolerance dimensions, only one of them shows up as 37'-10". The rest show up as 37'-9". This prompts two questions--first, why is Revit ever rounding down with a 1/2" dimension at a 1" tolerance? And secondly, why is is there a different result for the same measurement depending on its location?

I've double and triple checked the exact dimensions, using the measure tool, a 1/256" tolerance dimension, and verifying the actual value in the dimension itself as well as in the properties tab. They are each exactly 37'-9 1/2". So it's not an issue of the model being incorrect or imprecise. See the attached image; the dimension string on top is the 1" tolerance dimension, while the individual dimensions below are 1/256" tolerance.

Re: Dimension rounding error

mphungDCHNW — Mon, 04 Apr 2022 20:58:28 GMT

If you want you can always change the dimension to the desired length manually.

Re: Dimension rounding error

barthbradley — Mon, 04 Apr 2022 22:58:21 GMT

Post your file here.

...if you don't want to show fractional measurements, why don't you document this way:

Based on your explanation, it sounds like you want to communicate the equality of the bays, rather than the actual measurement. I wouldn't have the bays measuring different widths in different views in the same CDs. That's a recipe for error.

...the other option would be to drop the dimensions from the elevation views; not show them at all. I mean, what's the purpose of showing them - especially if they aren't dead on ballz accurate?

Re: Dimension rounding error

jbrr27 — Mon, 04 Apr 2022 23:27:17 GMT

The dimension already IS the desired length, so there's no need to change the actual dimension. If you mean manually overriding the text of the dimension, that is a possible workaround, which I may use If I can't figure out why it's happening. The reason for my post, however, is that I'm more interested in getting to the root of the problem. Why is it happening in the first place?

Re: Dimension rounding error

jbrr27 — Mon, 04 Apr 2022 23:26:51 GMT

I'll see if I can get a cleaned-up version of the model posted. Right now I have to get them submitted ASAP.

The purpose of the dimensions is to show compliance with city regulations on variations in height and wall plane, so they are necessary, and do need to show a specific number. They have to be shown on elevation as that's all that's being submitted at this point. But the issue occurs in plan view as well. The tolerance isn't critical, since all I have to show is that it's under 50' or whatever the requirement is. When it gets to CDs, I'd be using a higher precision of dimension, so the problem goes away. It only occurs at 1" tolerance.

At this point, I'm not so much looking for a way to get it to appear correctly. I can do that by overriding the text, or changing the tolerance and living with fractions. It's more about figuring out why it happened to begin with.

Re: Dimension rounding error

barthbradley — Mon, 04 Apr 2022 23:53:59 GMT

Do this (or not):

PIN the Model. Pull a continuous dimension string to/from each bay. Click on "EQ". Does it work or error out? If it errors out, then your bays aren't equally spaced.

Re: Dimension rounding error

jbrr27 — Tue, 05 Apr 2022 00:10:46 GMT

They bays are not adjacent, so you can't pull an equal dimension as far as I remember. See the image in the original post. As stated there, I put a 1/256" tolerance dimension on them, and they are exactly 39'-9 1/2". This is confirmed by the reading in the properties window, the reading clicking on the dimension, and using the measure tool. If they're not exactly the same dimension, it's by a fraction of an inch that's too small for Revit to read back. There's no other tool I'm aware of in Revit that would allow any other measurement to greater precision. Unless the equal dimension string can be used with non-adjacent measurements.

Re: Dimension rounding error

marybethP25M4 — Mon, 27 Oct 2025 14:38:34 GMT

Did you ever figure out a solution? I am having a similar error. A dimension of 40' - 3/4" measuring two areas of a building is rounding differently. I am using the same dimension type and have confirmed the true dimensions are the exact same. One rounds to 40' - 1", the other to 40' - 1/2".

Re: Dimension rounding error

jbrr27 — Mon, 27 Oct 2025 22:31:06 GMT

I didn't. I've come across this at least one other time since, but never did find out why it was happening.