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I'm very new to Blender, and I'm confused by scale and dimension. If I create a cube with the scene length unit set to inches, I get a 24" cube. It's 2m if I leave the default units.

If I change the dimensions, it changes the scale. If I change the scale, it changes the dimensions.

I did see this question linked to this question, which links to a 404.

If I look up what Apply means, and it seems to basically mean "make all the non-destructive things you've done permanent a.k.a. destructive."

And it seems that scale is non-destructive but dimensions are destructive.

It's not clear why changing the scale changes the dimensions and vice versa. What's going on?

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Object and mesh are 2 different things. An object is a kind of shell that is defined by the mesh it contains and its 3 transformation datas (Location, Rotation, Scale). Even though when you create a new object it necessarily contains a precise mesh, you can later change this mesh for whatever mesh you want, for example several objects can share the same mesh.

Changing the scale of the object is not the same as changing the scale of the mesh:

If you change the scale of the mesh (in Edit mode), the change won't affect the object scale and it will be replicated on any other object that share the same mesh.

If you change the scale of the object (in Object mode), the mesh remains the same even though it appears stretched in your scene, it's only the object scale that has been changed, and the mesh won't appear stretched in any other object that would share it. If you take a look into the N panel you'll see that the Scale value is not 1:1:1 anymore. If you want to reset its scale back to 1:1:1, press AltS. If you want to make its current dimenions its new 1:1:1, apply the scale with CtrlA, but in that case it will definitely change the scale of the mesh itself.

Scale will only take into account the scale that you've made in Object mode, while Dimensions will take into account whatever changes you've made, whether it is in Object mode or in Edit mode.

To sum it up, Scale is relative to the object itself while Dimensions is relative to the scene unit.

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    $\begingroup$ I would add that the user should always work with a scale of 111 (so scale should always be applied to objects), because if not every measure in edit mode will be wrongly reported, and many functions and modifiers could behave in weird ways. In example: create a cube, set its dimensions of the desired sizes, press Ctrl A > Apply scale. $\endgroup$ Sep 3, 2022 at 7:48
  • $\begingroup$ Thank you for the thorough answer @moonboots. If I could summarize for my own clarity, every object has an innate size based on it's corresponding mesh. You can change the size of the object non-destructively using scale, which is a percent of its innate size. For convenience, you can also use scene units to express a scale change. Once the change in object scale is applied, the coordinates of the vertices is calculated, the "innate" size changes, and that becomes the new "100%". Does that sound about right? $\endgroup$
    – Becca
    Sep 4, 2022 at 3:28
  • $\begingroup$ yes that's it ;) $\endgroup$
    – moonboots
    Sep 4, 2022 at 4:33

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