What are the real world dimensions of bricks? (starting with 1x1 brick) Plates? Studs? Does LEGO think of this in metric or imperial units or something else?
This image shows the dimensions in LEGO Units. 1 Lego Unit is 1.6mm (the thickness of the plastic wall). In those units the stud's diameter is 3 (= 4.8mm).
This image from Brickipedia should sum it up nicely:
A plate is exactly one third of a brick in height (3.2 mm as in the diagram). In other words, 3 plates stack to match the height of a brick. This is useful to know if you're short on a certain size of brick, but have enough plates of the same shape and color to cover it in height.
While LEGO uses metric nowadays, you may be interested to know that the bricks they originally copied (and bought the patent for later on) were made in the UK and thus probably used imperial measurements (although dimensions are not specified in the original patent). You may want to search for UK patent 529580 or Kiddicraft to learn more about this. There may still be remnants of that English heritage buried deep in the LEGO legacy.
Also, when LEGO started, I'm not sure what their measurements or tolerance were at the time, but they probably weren't as strict as they are now, which may account for some oddities in the system. For example, the distance between studs has been measured as 7.986mm rather than an exact 8mm.
Robert Cailliau has summarized how dimensions of LEGO bricks derive from:
- The base measure 0.8mm (that's where the 1.6mm already mentioned derives from)
- The play measures 0.1mm (for additional space between pieces)
- The height of studs 1.8mm
It looks like the number as the same as given in other sources, but there is disagreement about the height of a stud. I've seen the value 1.8mm (Robert), 1.7mm (Wikipedia) and 1.6mm (answers given here). Maybe the difference is because of the "LEGO" logo on top of a stud.
The precise measurements with an easy to understand technical drawing is available here. A PDF with the all the dimension is available for download.