First a general note: even the Nihon Ki-in rules do not specify exactly which sizes must be used (apparently, the phraseology is "is usually..."). From this, one can infer that the actual sizes are not of immense importance. The numbers here will not be agreed on by everyone either (see the discussion below). The following measurements are one version of Japanese standard dimensions. The board thickness is for a floor board.
A 19x19 board should measure 454.5 mm by 424.2 mm. It should be 151.5 mm thick.
The lines are typically 1 mm thick. They should be spaced 22 mm apart left to right and 23.7 mm apart top to bottom.
Star point markers are typically 4 mm in diameter.
There should be 181 black stones and 180 white stones, which should be between 6 and 10 mm thick. White stones should have a diameter of 22.1 mm. Black stones should be slightly larger. The stones are bi-convex, which is to say curved outward (bulging) on both sides, like a magnifying lens. However, the rim should have a soft edge; they shouldn't be "sharp".
Just for completeness, the following table recapitulates this information in other measurement units:
Dimension SI Imperial Japanese (mm) (inch) Board width 424.2 16 23/32 1.4 shaku 尺 Board length 454.5 17 29/32 1.5 shaku 尺 Board thickness 151.5 5 31/32 0.5 shaku 尺 Line spacing width-wise 22 7/8 7.26 bu 分 Line spacing length-wise 23.7 15/16 7.82 bu 分 Line thickness 1 1/32 0.3 bu 分 Star point marker diameter 4 5/32 1.2 bu 分 Stone diameter 22.5 29/32 7.5 bu 分
(1 inch = 25.4 mm. 1 shaku = 100 bu = 303 mm.)
You can view a beautiful example of a board made using the above specifications.
Experimentally measured go stone dimensions for several glass, yunzi and slate and shell stone sets were discussed in the "Comparative measurements of go stones" thread on godiscussions.com.
ikktomuseyokkis these dimensions seem off to me... 22*18 plus 19 lines does not equal 424.2...
Bass: ikktomuseyokkis, you are correct, they do not (and should not) add up; you don't want to be balancing the first line stones on the edge of the board, there needs to be some extra space around the grid for that reason. Also, "line spacing" is a slightly unfortunate wording here, what it means is that there is a 1 mm thick line every 22 mm. (It does not mean that you should measure 22 mm from the edge of the line to the edge of the next line.) Yes, this means that the stones will not fit the grid in a perfectly straight line, and yes, afaik, this is intentional.
A Go board is not meant to be square. When seated in front of a square board, it would look wider than tall. Therefore, for reasons of perspective, they are longer in the direction from one player to the other than from left to right. 
Black stones are slightly larger than the white stones to compensate for an optical illusion which would otherwise make the white stones look slightly larger than the black stones.
The stones should be slightly larger than the left-to-right line spacing, which keeps them from being placed perfectly regularly on the board. This is for aesthetics; the far east culture traditionally does not like symmetry.
The stone thickness is a matter of taste. There are Chinese type stones that are so-called "single convex" (or "SC"), meaning that there is an outward curvature on only one side of the stone, while the other side is flat. This creates a "right-side-up" aesthetic that is absent in Japanese style stones; the player places the stone with the flat side down against the board. An example of these are Yunzi type stones.
The board thickness given is for a floor board. The floor board typically has legs which are roughly 10 cm (4 inches) high, so that the playing surface is around 25 cm (10 inches) high. Playing on floor boards means that you sit on the floor, possibly with an armrest. Often, table boards are used (placed on top of a table). Table boards can be up to 5 cm (2 inches) thick.
There are no size requirements for bowls. Suffice it to say, they need to be large enough to carry all the stones. A lid is useful to temporarily store captured stones.
BobMcGuigan: When using floor boards with legs, it is customary in Japan for the bowl to be placed on the floor between the player and the board, and slightly underneath the board. Therefore, bowls should be properly sized to fit underneath the floor board.
StormCrow: That's because you're seeing the board from the side, not from the perspective of the players.
bkhl: I wouldn't think so. If that were the case it would hardly be made so that the rectangles look square from the players' perspective.
protognsis?: The length spacing would need to be more than 15/16ths in order for the board to look square from the player's perspective. Also, it varies A LOT based on the angle of depression from the person's eye level to the board.
Matthias: If my calculations are correct, this works for an angle of 68 degrees (where 90 degrees would be looking straight down from above the board). That may be a little higher than a normal playing position, but I guess the subjective perception is also influenced by the brain that realizes it is not looking straight at the board. Also, if the length spacing would be increased, if would be hard to play with round stones, as the distance between two stones next to each other would vary too much.
Xezlec? Dislike of symmetry? But... isn't the whole game designed to be as symmetrical as possible? It's a big square made of little squares, and they're even spaced so as to make them look more symmetrical from a certain perspective. The stones are circles, and even the shell ones are cut so as to make the lines on them as straight as possible. The star points and the rules of play are also symmetrical. I was drawn to Go because it is seemingly the most symmetrical game in the world. Surely it must be a certain kind of symmetry that they dislike, and not just symmetry in general?
Randall: I had trouble finding this page just now. (I'm about to buy some cheap equipment and I wanted to check what SL had to tell me about regulations sizes.) Had I not been so confident that it must exist, I would have given up before finding it. Equipment is the right word, but it wasn't the first thing that came to my mind. I searched for board, stones, regulation, and size. I don't know how hard it is to make the page easier to find -- perhaps people just need to be cleverer than or as persistent as I am.
Random passerby: Because of the above comment, a Google search for "regulation size goban" (without quotes) will now pull up this page. That's how I got here.
mdh Can anyone post the measurements for a Chinese style board. I have been told that it is larger and the cells are square.
Pashley I'm in China. Boards here are typically square. Most boards, bowls and stones you see are pretty basic. Often there is a go board on one side, xiangqi (Chinese chess) on the other. Stones are flat on one side and sold in wicker basket bowls.
There are nicer boards around. I bought the commonest variety of these for about $100 US. They have the overall shape and decorated sides of a Chinese tea tray in a fairly dark wood, with the lines and star points inlaid in mother-of-pearl.
Board is not to hand. I'll post measurements later.
Derek? I'm not in China, but Vancouver, Canada, which is about 1/3 ethnic Chinese. Inexpensive Chinese-made Weiqi boards are easy to find, and all look alike---most with Xiangqi on the reverse side, some are traditional dark cherry stained softwood with faux-mother-of-pearl decoration. The boards appear perfectly square until you take your ruler to them:
The grid itself is 420mm wide by 436mm long (cells are 23.33mm by 24.22mm)
These are designed for Chinese-style stones (flat on one side, 23mm diameter), which lay across the board beautifully---with barely visible gaps from side edge to side edge, and only a little more from top to bottom.
The blue or yellow plastic fold-up boards that often come with stones aren't really consistent in dimension; but most are perfectly square, with cells about 436mm and up. It's a mystery to me why the plastic boards are so unusually shaped.
Rick? Many inexpensive boards sold in the USA have perfect squares, because American beginners expect that and will sometimes return boards to stores if the stones don't fit evenly on the board. If they notice that the board is asymmetrical, they may believe that it is a printing error. Large retailers do not have knowledgeable staff who understand and can explain the reason for the non-square boards, so the store's buyers prefer & request square boards. Americans, in general, do not usually admire asymmetry. I'm a GO retailer, and we've seen this happen many, many times over the last several decades. Funny, but true!
A great usenet post on (Japanese) board dimensions can be found here: http://www.gungfu.de/go/gobans/texte/Goban%20dimensions,%20a%20summary ( rgg)
Ender: Does anyone know of a walkthrough somewhere or have an idea of how to make your own stones from the slate and clam raw materials? I would imagine that it would be much less expensive than buyin them pre crafted...
Zarlan: I would imagine that it would, in fact, be much more expensive, unless you intend to make a very large amount of them.
mysticmonk? Have a set of Yunzi stones from China. They are slightly larger then the japanese standard. Does anyone know where you can find boards for these? It came with a Vinyl board that measures a little larger then my goban.
This site sells a board of the appropriate size:
Pashley Chinese stones have an advantage in some teaching games or friendly games where you want to have a discussion along the lines of "If B plays here, and W there, then ...". You can play a series of stones upside down -- flat surface up -- for discussion. When you're done, it is easy to remove the inverted stones and go back to the original position.
uxs: I just acquired some pyrex bowls. The label says they're 0.6L. They fit perfectly for holding a complete set of korean stones, size approximately 22mm x 8.5. I do have to put 10 black stones in with the whites, because of the size difference.
FredA?: www.go-gamestore.com sells chinese size boards, but they just ship to USA and Canada, does anyone know of some online shop that ships to Europe AND that sells boards of the appropriate size for chinese yunzi stones ?
[T & T]: What is the equipment dimension for Japanese Standard Size and Chinese Standard Size? Lines spacing? Never mind board thickness. Anybody know?
qukk?: Would Chinese stones fit on a grid with the above dimensions?
AshR?: Which way along the board should the grain of the wood traditionally be orientated? Along the longer dimension of the goban or with the shorter side?
Traditionally the grain on the top face of the board runs with the longer dimension.
justdidit?: Well they are 3 different sizes of goban according with the countries, one for China, one for Japan and one for Korea, from the bigger to the smaller. thats important if you want a goban on which your stones will fit well. If you use chinese stones on a korean board, you will be in a mess, and if you use korean stones on a chinese board you will find them quite small.