Diamond Weight Estimate for Marquise Cut

Length-to-width adjustments (LWA) for weight estimation formula. The LWA is used in all marquis weight estimation formulas.
L/W ratio LWA
1.50/1.00 .00565
1.75/1.00 .00570
2.00/1.00 .00580
2.25/1.00 .00583
2.50/1.00 .00585
2.75/1.00 .00590
3.00/1.00 .00595

Marquis Formula:

Length x Width x Depth x LWA x GTA

1) Example of formula in use:

Length measurement: 10.24 mm
Width measurement: 6.11 mm
Depth measurement: 4.75 mm
Girdle: Thick+

L/W Ratio: 10.24 divided by 6.11 (length divided by width) = 1.6759, rounded up to 1.68 to 1. Referring to the previous LWA list for marquis diamonds, notice that the 1.68 L/W ratio is closest to the 1.75/1.00 case, so this will set the LWA in the formula.

Since the girdle average was determined to be Thick+, then referring to the GTA table (p. 137), 1.035 will be assigned as the GTA multiplier in the formula. For diameter, use the width of the fancy shape, not the length, in choosing the correct column of GTA multipliers.

Formula will read:

10.24 x 6.11 x 4.75 x .0057 (LWA) x 1.035 (GTA) = 1.753 rounded to 1.75

2) Example of formula in use:

Length measurement: 6.23 mm
Width measurement: 3.25 mm
Depth measurement: 1.90 mm
Girdle: Extremely Thick

L/W Ratio: 5.23 divided by 2.03 = 2.576 rounded up to 2.58 This is closest to the 2.50/1.00 example so the LWA is .00585

Since the girdle average was determined Extremely Thick-, referring to the GTA list for a 3.25 mm width measurement the GTA is 1.09.

Formula will read:

6.23 x 3.25 x 1.90 x .00585 (LWA) x 1.09 (GTA) = .2453

Rounded to *.24 ct.

*Always round the weight down in the final estimation unless the third digit (1/10th of a point) is .009 or higher. Example: .2453 would be rounded to 0.24 and .2491 would be rounded to 0.25.

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