In determining the right size chess board square,  there is the easy method, and a more complicated method.  The easy method is just this:  take the diameter of the king base, and add ¼” to it, or more if you like.  Or, as a general rule of thumb, take 0.75 and divide it into the king base diameter.  The answer you get in both cases would be the size of the chess board square you`re looking for.  If the answer does not correspond to a standard size for a chess board square (and it probably won`t), then select the next highest standard size.  Another easy way is to use what the FIDE ( International Chess Federation) has stipulated.  The FIDE  equipment standards say that the size of the chess board square should be twice the diameter of a pawn.  And now for the more involved method…

The United States Chess Federation  (USCF), in rule 41C,  mandates that the size of the chess board square for tournament play be determined as follows:  the size of the king base should be around 0.78 percent the size of the chess board square.  This is to ensure that there is plenty of space-but not too much-between the pieces, so the players don`t begin to see a blur and become confused.  The range for the size of the king base is usually given (although not by the USCF) as:  0.75 to 0.80 percent of the size of the chess board square.  Note that the average of this range of values is 0.78.  Here is what you you should do:

1. Measure the diameter of the round end of the king-also known as the “king base”.

2. Take that number, and divide it by the 0.78 from above.

3. The answer you get will be the size of the chess board square you are looking for.

4. If the answer does not fall on the size of a standard chess board square, simply select the        next highest size chess board square for your chess pieces.  It is important to note that you should select the next highest, not the next lowest, to ensure proper spacing between the pieces.

5. You may also do the calculation by multiplication, if you desire.  Just take the reciprocal of 0.78 and multiply it by the diameter of the king base.  The reciprocal of 0.78 is:  1/0.78 = 1.28

6. To make clear the above explanation, I shall give the following example:

I have a tournament style Staunton chess set  (with a vinyl roll up chess mat) at home.  With a tape measure I measured the king base to be:  1.5″.   Ok, so what size chess board square should I have?  Well, from #2 above  I would perform the following calculation:  (1.5)/0.78=  1.92 or rounded off:  2″   What this means is that 2″ is the mid-range size for the chess board square, and is probably the value I would go with.    As it turns out the size of the chess board square I actually have is  2-1/4″.

Now let`s take a look at the same example using the reciprocal method from #5 above.  Take the diameter of the king base, and multiply by the reciprocal of 0.78, which is 1.28:

(1.5) x (1.28)= 1.92 or 2″ rounded off.

If you already have a chess board, but not the pieces, simply reverse the above process.  Take the size of the chess board square and multiply it by 0.78, or divide it by 1.28, and this will give you the correct mid-range size for the king base.  The calculations are done with the king base, because the king is the largest piece on the board, so if the size of the chess board square is found using the king, all the other pieces will also be correct.