Rhino Dimensions always slightly wrong

Hello All,

Just switched from Rhino 5 for windows to Rhino 6. I used to have the same issue with the windows but not as regularly as the mac version. All of my dimensions seem to be really inaccurate or rather too accurate.

When something has been drawn at exactly 20mm for example the dimension will read 19.89 or something similar. Very disconcerting if this is to be sent for manufacture of production. Is the drawing wrong or is the dimension set up incorrect?

Any bright ideas welcome. Need a solution!!!

We need an example!

Without a specific example, it’s impossible to guess.

It could easily be some combination of the named dimension style settings, and how you are using Osnaps to select points.

Please post a simple example of some dimension and the geometry it is referencing, and we’ll take a look.

Obviously I can’t speak for your examples, but after having used Rhino for years and years I have never encountered this behavior. If I draw something at 20mm It is exactly 20mm. Would be interesting to see an example for sure.

1 Like

I have run into something that has gotten me into trouble before. There is a dim properties setting called Length Factor, which is in the Length Units settings. I have my Properties window docked to the right of the screen, and I have mistakenly used the scroll wheel to scroll down through the various dim attributes. If your cursor happens to pass over this Length Factor field while you’re scrolling it will change the value accidentally.

This has caused embarrassingly errored drawings more than once until I investigated the problem. I’ve learned not to do that but I would suggest to McNeel to require an extra click or checkbox or something to prevent such a potentially dangerous inadvertent settings change.

I do not know if this has anything to do with your issue but it sounds plausible.

Wow… I cannot make this happen right now in the latest - I have to be deliberately clicked into the number field to get scrolling to do anything there - can you repeat what you describe ‘casually’ so to speak?


Yes. Just did it again to verify. I have both my Layers window and Properties window docked to the side of my screen, one over the other. For the sake of demonstration, highlight any dimension, then expand all the dim properties sub-menus by clicking on their arrows in the properties window (> Dimension Lines, > Arrows, > Length Units, etc.) .

The mouse scroll wheel will scroll the Dimensions menu as long as the cursor is somewhere over it. If your cursor happens to be near the right side of this menu then the value fields will pass by underneath your cursor as you scroll. The moment a field is under the cursor, the window continues to scroll but it is also changing the value in the field as it passes underneath your cursor. So the scroll wheel is doing two things at once; scrolling the window and changing the values.

You will see the Title of the values turn blue to indicate they have been changed, but if you’re not looking for or expecting that behavior, you will have no way of knowing that anything just got changed.

This has caused some very costly mistakes in our manufacturing, and drove me nuts until I learned what the source of the dimension errors were. As a precaution now I will do a SelDim and check the Length Factors globally to be sure they are all set to 1.

Hi Brian - On my machine, right now, I cannot reproduce this - it rings a faint bell though - can you tell me what Service Release of Rhino you are running (SystemInfo command)


Rhino 6 SR16 2019-7-9 (Rhino 6, 6.16.19190.07001, Git hash:master @ a8b4ee102e9e0eb1d11825df063e13f96d518f93)
License type: Commercial, build 2019-07-09
License details: Cloud Zoo. In use by: Brian Jackson ()

Windows 10.0 SR0.0 or greater (Physical RAM: 32Gb)
Machine name: DESKTOP-KIR2S4R

Non-hybrid graphics.
Primary display and OpenGL: NVIDIA GeForce GTX 1070 (NVidia) Memory: 8GB, Driver date: 4-17-2019 (M-D-Y). OpenGL Ver: 4.6.0 NVIDIA 430.39

OpenGL Settings
Safe mode: Off
Use accelerated hardware modes: On
Redraw scene when viewports are exposed: On

Anti-alias mode: 4x
Mip Map Filtering: Linear
Anisotropic Filtering Mode: Height

Vendor Name: NVIDIA Corporation
Render version: 4.6
Shading Language: 4.60 NVIDIA
Driver Date: 4-17-2019
Driver Version:
Maximum Texture size: 32768 x 32768
Z-Buffer depth: 24 bits
Maximum Viewport size: 32768 x 32768
Total Video Memory: 8 GB

Hi Brian - can you please update to sr 17 and see if that behavior is any different?



I will. Will get back to this topic tomorrow. Thanks for following up on this. Perhaps this is the original poster’s issue.

Hi John,

Thank you getting back in touch its great to get so many responses!!! Please see the attached image. I think it demonstrates what i mean, but please let me know if i can provide you with more information.

So we’re just doing dimensions drawings and it sometimes sees to do this. My colleague had ‘near’ on so i always thought it was that but then it started happening to me once i went to the mac version.

Hi Mark,

Thanks for your help. Please see the image above.

Hello - are you placing the dimensions using Near and Perp or just Near? Dim or DimAligned? Are the curves flat, 2d, parallel to or in the construction plane?

@christianwatson.cw - better to post an example file.



I am using perpendicular but not near. I never really use near as it seems to get me in more trouble than it is worth. I usually just type in dim so i imagine dim. They are flat after using make2d.

Ok sample file attached.

Dimensions in blue are the ones that are the tricky ones. Others are fine.
Please don’t judge me too hard on my drawing!!! Not the most proficient of users. @pascal


Hello - I am not able to get any different numbers than what you have…



What am I looking for, exactly on the blue guys? Distance reports back the same numbers…


I, too, cannot recreate the problem. But I did notice that in your first example image that the lower line didn’t appear exactly horizontal when I zoomed in and panned the line to the bottom of the image viewer window. It looked like it was angled ever so slightly in a direction consistent with your dimensions. Are you doing a Make2D to generate the 2D linework? Just curious.

1 Like

Hi @pascal,

So the issue is that when we drew it it wasn’t those dimensions.So this is an example of how the file is reading it and saying its 200.50 yet we drew it at 200? Does that make sense? I can try and find another file if you like?

Hi @brianj1

So im doing Make 2d and dimensioning off of that? Is that ok?

Hello - I guess what I’d like is the file in your image above a few posts where there are two different dimensions on the same bit of seemingly parallel geometry.
For the file that you did post, are you saying the 3d object is 200 (say) and Make2d of it is off by a half unit? Your 3d object is 200.5 as far as I can see.