The stone is positioned in the standard orientation, that is, with its table horizontal and facing downwards. The model diameter is measured in 360 directions with the step of 0.5°, because opposite directions apply to the same diameter. The diameter of the model in some given direction is measured as a distance between two parallel vertical planes placed perpendicularly to the given direction as close to each other as possible, so that all vertices of the model lay between these planes. Width and length are are calculated from this array of values as follows, dependent on the particular cut.

Round brilliant

• Width is the Minimum diameter
• Length is the Maximum diameter

Rounded Fancies / Marquise, Oval, Pear

• Length is the Maximum diameter
• Width is the minimum diameter in the direction perpendicular to Length ± 10°

Rectangular Fancies / Princess, Radiant

• Width is the Minimum diameter
• Length is the minimum diameter in the direction perpendicular to Width ± 10°

StepCuts / Emerald

• Width is the Minimum diameter
• Length is the minimum diameter in the direction perpendicular to Width ± 10°

Stepcuts / Trapezium

• Length is measurement as local diameter minimum parallel to axis symmetry direction (+\-10 degrees)
• Width is measurement as local diameter  maximum perpendicular to axis symmetry direction (+\-5 degrees)
• Please see Trapezoid Length, Width and some other parameters calculation for more information

Triangle

• Measure the diameters of the model in the direction of all 3 sides.
  
  
  
  
• The measurements are ordered by an increase as D1 < D2 < D3.
• Which measurement is most different from the other two becomes the base (width). Math: if D2/D1 > D3/D2, then the width is D1, otherwise the width is D3.
  
• The perpendicular direction becomes the length.

Trilliant

• Distances between the three outermost vertices of the projection are measured. (The outermost vertices are defined as those touching the minimal circumscribed circle.)
  
• Distances are ordered by increase as D1 < D2 < D3.
• If D2/D1 > D3/D2, then Width = D1, otherwise Width = D3. 
• Length is defined as the diameter of the model in the direction perpendicular to Width.
• Table width is defined as the maximum distance between table vertices in the direction of Width +/- 10°.
• The table vertex farthest away from the Width line is found.
  
• Table length is defined as the maximum distance from that vertex to another table vertex in the direction of Length +/- 10°.
  

Unknown cuts

• Width is the Minimum diameter
• Length is the extremum (minimum or maximum) diameter in the direction perpendicular to Width ± 10°