The labyrinth reflects deliberate principles of sacred geometry, especially regarding the numbers three (trinity, soul, divine) and four (body, earth, this world). These two numbers can be combined, symbolizing the integration of body and spirit, physical and divine. Added, they give seven and multiplied, they give twelve. Both numbers are important to the Chartres labyrinth.
To draw the 11 circuits (paths) in the labyrinth requires 12 circles. Below is a summary of the proportions of the labyrinth as determined by Robert Ferré. Agreement on this subject is far from universal. For example, Robert has determined that Keith Critchlow's oft-repeated theory of an invisible13-pointed star in the labyrinth is incorrect. Because the stones are worn and there is mortar between them, measuring the Chartres labyrinth is rather complicated. The proportions below are a composite taken from careful examination. If you follow these specifications exactly, there will still be an error somewhat under one percent with regards to the actual labyrinth. But that's pretty close.
The measurements below take into consideration that lines have width. In Chartres Cathedral, the lines of the labyrinth are three inches wide. Therefore, there is an inside and an outside dimension of each line, which is to say, one side is closer to the center and the other side, further away (and therefore, slightly larger). The proportions will specify to what part of the line the measurements pertain. "Inner" or "inside" mean closer to the center;"outer" or "outside" mean the opposite (further away).
Center Circle: The center is one-fourth
the diameter of the labyrinth, measuring from the outside of the center
circle to the outside of the 12th circle (not including the
lunations, the small partial-circles around the perimeter).
Petal: The outer petal circle
is one-third the diameter of the outer center circle. (Note the fours
and threes. The center is one-fourth, the petals are one-third. Could
the center be this world, and the petals represent Mary?)
Path: The width of the path, not
including the line, equals one-third the diameter of the petal.
Line: The width of the line is
very important. The line and path together comprise 11 units, of which
the line equals two units and the path nine. Once you have the path width,
you can divide it by 4.5 to get the line width, or divide it by nine (which
gives one unit) and multiply that result by two (hence, two units). In
other words, divide the path width by nine and multiply that number by
two and you will find the line width.
Lunation: The spacing of the lunations (the circles around the perimeter, measured mid-circle to mid-circle) equals the width of the path. (Example: 12 inches.) However, the lunations require a little fudging, in order to get a tooth at the very top, on the vertical axis. As a result the lunations on the left side are slightly closer together and the ones on the right side slightly further apart. The top tooth is number 56. There are 55 lunations on the left side and 57 on the right side, for a total of 113 teeth. The teeth on either side of the entrance are half the path width from the entrance (Example: 6 inches.) Want to be more mathematical? Calculate the circumference and divide by 114. This will find the spacing on the 12th circle, rather than through the center of the lunation circles. The diameter of 36 feet equals 432 inches. Times pi (3.14159), we get a circumference of 1357.17 inches. Dividing by 114, we get 11.9 inches, or about 3/32 short of our previous estimate of 12 inches. As I said, this number should be a bit smaller on the left side and a bit larger on the right (by 1/8 to 3/16 inches).
Note that the path width is one-third of the petals which are one-third of the center which is one-fourth of the diameter of the labyrinth. That comes out to being 1/36 the diameter of the labyrinth. If you have a Chartres labyrinth that does not follow the correct proportions, you won't be able to calculate the lunations by the method given here. Instead, just divide the diameter of the labyrinth by 36 and use that measurement for your spacing (not counting the minor fudging).
Although I have given an example, these measurements apply to any size Chartres labyrinth. If the diameter is 60 feet, the center is 15 feet, etc.
Periodically I receive a call from someone who wants to make an exact-size replica of the Chartres labyrinth. Here are the actual measurements as I have personally made them in Chartres.
Diameter from tip of tooth to tip of tooth: 42' 3 3/8"
Diameter to outside of 12th circle, not counting lunations: 40' 4 5/8"
Diameter of center (to outside edge of the first circle): 10' 1 1/4"
Path width: 13 5/8" to 13 3/4"
Line width: Varies from 3" to 3 1/4" but most are close to 3"
Space between labryses (back-to-back turns): 3" to 3 1/2". I would use 3 1/4".
Lunation: Inside diameter of the circle: 11"
Lunation, total width: 13 3/4" (measured through the center of the circle, from mid-tooth to mid-tooth).