Spread is an estimate of a cut's face-up size for its weight, compared with a stone 61.5% deep. Above 100 means the cut faces up larger for its weight than that reference.
In more detail
Weight goes with the cube of the diameter, so the formula uses the cube root of the depth ratio. Spread estimates from depth alone. The face-up size on our gemstone cut pages is measured from each model's outline instead.
How we measure it
Spread = min(130, 100 × (61.5 ÷ depth)^(1/3)), with depth as a percentage of the width. It is the same in every gemstone. The Cut Performance Wheel draws values above 100 on its 100 ring and lists the true figure.
Related terms
- Face-up size: Face-up size is how large a stone looks from above for its weight. Two stones of the same carat weight can differ in face-up size because of their depth and shape.
- Overall score: The overall score is one figure out of 100 that combines our light-performance scores for one cut in one gemstone. The Cut Performance Wheel calls it Global.
- Cut Performance Wheel: The Cut Performance Wheel is a free Digital Gemology tool. It draws eight light-performance scores of one cut, in one gemstone, on a wheel.
- Total depth: Total depth is the height of a stone from table to culet as a percentage of its average diameter. It equals crown height + girdle thickness + pavilion depth.
- Carat weight: Carat weight is the weight of a gemstone. One carat is 200 milligrams, a fifth of a gram, and it has 100 points.