hi
I am currently learning about 3d printing
firstly,
I'm sorry if this topic is a repost (i'm new member and I dont know lot of tutorial that have been posted )
secondly,
I'm posting this because some people might still have problem with dimension error when output his design into stl file
ok, lets go to the point :)
I know some of you have 'problems' with scale error when making 3d files, specially when you work with different software (3dsmax -> goz zbrush / dazd)
we will often get scaling error . why ??
because each software have their 'own units setting' (so the scale of your model will change if you not exporting in correct setting)
I won't give further explanation about this units (I don't know how to explain it --> lollollol)
i will just show you a very 'simple' way to correct this problems
lets just say I'm creating box with 20mmx10mmx10mm
this box

then , I'm gonna export this box as STL.

and try to put in my printing software ( I'm using repetier host)

and.. WTH? why is my box so small???
argh , lets fix this!! :D
I know that my dimension is correct (10x20x10) / (1x2x1)
so, in this case im just have to 'scale' it right?
okay . here is the tool that i'm using
the name is [Autodesk Meshmixer]
you can download it here
http://www.meshmixer.com/download.html
lets just open our stl file in meshmixer (klik import / drag-drop your stl file)

and re'scale' it by clicking Analysis -> Units/Scale

now we know the 'real' dimension of our box, its 0.787mm x 0.393mm x 0.393mm!!! (lol)

just scale it to the dimension that we want (10mmx20mmx10mm)
I know the longest part (0.787) is 20mm
when I put 20 and press enter, the other will fit automatically

klick done
now we get our 10x20x10 box now! (im so happy that my box now is in correct scale - tears)
now we can export this file (as stl)

and see if its is in the correct scale

now our scale are corrected. (each grid is 10mmx10mm)

sorry for my bad english
I hope this tutorial will useful for you
Happy 3d printing!!!
note :
with mesh mixer, you can also do = mesh repair / remesh / orientation / add support structure / cut / and lot of other fun thing
I think this is powerfull tool