I know the unit in Blender are arbitrary, e.g. you can have one unit represent 1cm, 1ft or 1 mile.

I'd like to know if there's an advised (community or otherwise) scale that I should work to.

Are there any issues that might occur from basing your scale too high or too low. e.g. 1 unit = 1mm or 1 unit = 1km?

  • $\begingroup$ You can change the scale to be metric or imperial in Properties->Scene->units and work in real world sizes. Otherwise you can assume any arbitrary scale you want depending on what is it you are trying to model. Are you trying to modeling atoms, jewelery, people, buildings, landscapes, planets or what? Note that if you are going to work on a 3d Printer or export to other software your choice of units might be very important. $\endgroup$ – user1853 Oct 23 '14 at 22:16
  • $\begingroup$ It depends, if this only about modelling then you could chose any scale. But when you try to assemble your models in a scene they should have the same scale. Problems could occur with physics simulation when gravity and mass are involved objects would behave differently. $\endgroup$ – stacker Oct 23 '14 at 22:22
  • $\begingroup$ This is one of those times it would be good to have an answer from an experienced game developer(which I'm not). I know that many of them struggle with precision issues because of large scenes which have a huge contrast between what is really big and what is really small. <- like shadow map resolution compared to the size of a mountain chain; So if you have some things like mountains with numbers like 1000000.0 units. And then there are shadows with small numbers like .00001; once you perform math operations that combine these numbers, the smaller numbers can be damaged(loss of precision. $\endgroup$ – MarcClintDion Oct 24 '14 at 1:12

By default one BU = one meter. This is a pretty reasonable size to go by as a rough guideline.

If you are modeling artistically you probably don't need to worry about units too much, but you should try to keep everything from ending up very small or very large, which could cause clipping issues in the viewport, making it difficult to work with. Though if this does happen, it's not hard to scale everything up/down.

If you are working precisely with units, then you can always set them the way you want in Properties > Scene > Units:

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    $\begingroup$ Thanks @gandalf3, the viewport clipping was exactly the kind of advice I was looking for. $\endgroup$ – Braaant Oct 23 '14 at 22:52

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