Units model and layout, altering project to metric from inches ..could someone explain

Units layout and units model.
Nothing in level 1 training pdf or internet on what both these are.
I also couldnt see, searching through on the word ‘units’, anything about altering the projects units from inches to mm then back again. to scale or not to scale.
…and how to get the dimensions to show mm when units set to mm, and inches whehn units altered back to inches.

using Jeffs advice I chose not to scale.

I altered an inched project to mm so as to work with some plans for components marked in mm, and got my component 12 times bigger than it should be !

dimension for the existing item still said 63, and the created item said 760, having drawn the first at 63 inches wide then the second at 760mm wide, after going to properties, selecting word units and millimetres from the dropdown and no to scaling.
I see a units model and that is now millimetres, then I see a units>layout and that is still set to inches.

so do I have to alter both to mm, have I drawn my 760mm item in inches ?

Just what is layout units about ?

WHY IS IT…I can go to properties>units and select millimetres and no to scaling and yet still see inches in the dimensions ?


Use scale if the unit is created the correct size in the units being used, and you want to change the units and have the numerical dimensions change so that the physical size of the object stays the same.

Use do not scale if you want the units to change but the numerical dimensions not to change. An example of when to use do not scale would be if you start creating an object with units set to inches but thought they were set to mm.

heh, i might of said that backwards in that thread… i’m confused now too :confused:

units model = current units of your model file
units layout - current units of your page layouts. If you don’t use Rhino layouts as a means of printing to paper, you don’t need to worry about this setting.

The scale question:

If you answer “No” when changing the units, the NUMBERS will stay the same.
1" will then be 1mm in the model if you change from inches to mm. Your model will be 25.4 times smaller.

If you answer “Yes” when changing units the SIZE stays the same.
1" will then be 25.4mm in the model if you change from inches to mm Your model size stays exactly the same.



So when altering units in a project and wishing for the object to stay the same scale, not get any bigger or smaller, choose YES to scale.

Its a bit counter intuitive, but I shall pin that to the wall.

I am sure I am not alone finding I have plans drawn up in inches and also others in mm for the same object by different contributors.

However, having done that , I cant see the dimensions now, the numbers are microscopic, as are the arrow heads, no doubt other annotations would also be affected, how do we get rhino to simply alter the content, so 29.92 becomes 760 when toggling back and forth between mm and inches ?

Again to have to go making changes to all the dimensions each time we jump from mm to inches is :scream:


I’ve never understood why, when changing units, the model has to be scaled. If I draw a 1" cube and want change my units to mm I only need to change the “ruler” I’m using to measure it.
If I do this in Max and draw a 1" cube then change my units to mm the model doesn’t scale, only the units I’m using to measure it changes.

Its confused the life out of me so far, I steer clear, probably memorable now as its the complete opposite of what the brain expects to do.

and why do the dimensions numbers go microscopic, I cant see them any more,


'Cause Max isn’t CAD. The Max help actually warns you to NOT change your file units after starting a model, or to make details smaller than 1 of whatever your units are set to. That’s…quite different from CAD systems.

If you want to measure distances, enter values, or make drawings with dimensions in different units from your Rhino model, you can do that without changing the model units.

I was just using Max as an example. It seems to me that objects should be system units neutral. Meaning I can draw and object in something other than the default units and not have to scale it or import a object of a different units system and not have to scale it to match the system I’m in. Or I can change the units globally and not have to scale the model. I mean all units are convertible to each other so why the need to scale the model, why not scale the system? I did discover that a Rhino drawing set up in feet and inches will accept millimeters as input at the command line.

Well Max is specifically not a CAD product, and specifically has interface “units” settings separate from the actual “system units” because it’s handling of the system units sounds horrid, like it’s only single-precision or something.

You can enter any units you want separate from the units of the actual model, but for manufacturing purposes choice of modeling units is actually really important for having adequate tolerances for the downstream purpose of the model.

Of course much of the hassle in this thread seems to stem from working with DXF/DWG files imported from others, which is a constant pain for anyone who works with them (like myself) because long story short those formats are dumb.


and now reverting back to inches (not dxf etc ?..just paper plans from folk measuring things in their units they are used to, mm, when the item was built originally in inches)…and I get this, having had to alter the text height of my dims so I could see them again for as mentioned they went microscopic,

and when I make units mm again, I will have to alter dims again…

whats the way to keep the dims same size whilst flitting between mm and inch ?


Export your ideal dimension settings for Inches and MM. When you switch between units import the proper setting and apply it to all dimensions and set it to your current style


Ok, will try to follow that.
Wish there was a tick box retain annotation size proportional to model, as others are saying, why should all things change scale, and as I also see, mess up the dimensions and leaders and more.

So I must revisit annotation , re do all the settings to get them looking the same as in inches, then export it, then import it everytime I go to millimetres. I have a variety of settings I use, for small medium and large dimensions , so thats a lot of alterations.

I really would like to see Rhino simply scale them along with the rescaling its doing when I say yes to scale when I dont want it to rescale the model. This sentence alone displays the odd scaling need of not wishing to alter size of model !


To complicate things a bit more Steve…

Here is a straightforward way to flick back and forth with no need to adjust units.

Attached is a test file where you can import these example DimStyles into your current file, if you wish.

The default dimstyle ‘Millimeter Small’ is 1:10, set up ‘new’ dimstyles using that one as a base, one in mm and the other in inch - both will be 1:10 or change to whatever scale you wish to use.

Once you’re set up;
‘SetCurrentDimStyle’ to one of the newly created dimstyles
‘SelDim’ to select all the dimensions - assuming there is only one scale in the drawing - otherwise set the differently scaled dims to different layers and select ByLayer.
Once selected, change the dimstyle from the properties panel.

Dimstyle Test.3dm (66.0 KB)