What are the dimensions of a LEGO brick?
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).
+1 for **Lego Unit is 1.6mm** - thats the important part, everything else is based on this.
Here I clearly see what I've found by try-and-error - to connect vertical wall of bricks with vertically oriented long brick (with rails - https://bricks.stackexchange.com/questions/6316/what-is-the-purpose-of-this-plate-with-door-rail/6317) I had to have studs on the side of wall once in 5 bricks. 5 * height = 6 * width.
How much is the gap between bricks? Does this graphic take the gaps into account?
There has to be some play, otherwise it would be hard to wiggle the parts apart from each other.
@Joubarc's answer points to Robert Munafo's measurements showing an actual stud pitch of 7.985 mm or 0.015 mm (0.0006 in.).
One important note. The wall thickness varies! For plates and 1xn bricks, the wall thickness is 1.6 mm, as shown in pcantin's answer. For mxn bricks (where m>1) the thickness is closer to 1.2 mm with little nubs aligned with the studs, as shown in bartneck's answer.
@pcantin - Upon further analysis I believe there is definitely a allowance for play. None of my bricks are exactly integer width and length. Unfortunately I don't have enough reputation to answer this question. I measured 24 different bricks and plates. I believe the linear dimensions for width and height are exactly 8.00 mm * number of studs - 0.2 mm. When I apply this formula across my 48 measurements (24*2) I get a standard distribution of 0.016 mm. It also explains the 5.8*31.8 mm measurement from bartneck's answer
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.
I found this synopsis goes a lot further than what was generally known after the Tyco trial. There is even a thesis written on the topic.
@ErikOlson either that site is gone completely(http://www.historia.com.pt), or there's a typo(http://www.historia.com maybe). https://www.historia.com/legos/clones/texts/kiddicraft.htm doesn't exist either though. https://web.archive.org/web/20150908034033/https://www.historia.com.pt/legos/clones/texts/kiddicraft.htm might be the archived version.
I used LDraw long before I learned about TLG's official use of millimeters. At some point on my own I measured a regular baseplate as being (roughly) 10 inches wide. In LDraw one baseplate is 640 units wide. Thus originally (and I still do this today even though I know it's not correct) I visualized the LDraw system as having 64 units per inch, and a 1x1 brick being 5/16 inches wide and 3/8 inches tall (ignoring the gaps between bricks). 1/16 inches happens to be very close to 1.6mm.
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 stud height disagreement can be easily settled by examining a 1x1 headlight brick: The face with the headlight stud is inset by the 1.6mm base unit from the theoretical no-play boundary of the brick. If the stud was 1.6mm high, we should have no problem placing another brick in front of the headlight face. Even if the stud was 1.7mm high, the 0.1mm play would still allow this feat, albeit with a very tight fit. Experience shows, howerver, that we can't fit another standard brick in front of a headlight brick, indicating that the headlight stud (which is hollow, so no logo involved here) ha
Wouldn't the interior cavity and the knob need to have a clearance tolerance? Both the cavity and knob could not be 4.8 so either the knob is smaller or the side wall thickness is thinner to make for a larger opening. If you go by the graphic on Mr. Cailliau's website the side wall is 1.2 leaving a cavity of 5.4 based on the 7.8 overall dimension (8-.2=7.8). This leaves a tolerance of of .6 which is rather large. If you were to use Mr. Cailliau's clearance of .2 between mating parts the clearance diameter would be 5.2 leaving a side wall thickness of 1.3. Alternatively we could reduce bot by .