Conversions

U.S. Mesh FEPA
16/18 D-1181
18/20 D-1001
20/25 D-851
25/30 D-711
30/35 D-601
35/40 D-501
40/45 D-426
45/50 D-356
50/60 D-301
60/70 D-251
70/80 D-213
80/100 D-181
100/120 D-151
120/140 D-126
140/170 D-107
170/200 D-91
200/230 D-76
230/270 D-64
270/325 D-54
325/400 D-46
Wide Range
16/20 D-1182
20/30 D-852
30/40 D-602
40/50 D427
60/80 D252
Size Designation Normal Size Range
1/4 0-1/ 2
1/2 0-1
1 0-2
2 1-3
3 2-4
4 2-6
5 4-6
6 4-8
8 6-10
10 8-12
12 8-16
15 10-20
17 12-22
20 15-25
25 20-30
30 22-36
35 30-40
45 36-54
50 40-60
67 54-80
Wide Range
60 264
45 620
30 2,046
15 16,960
9 78,600
6 262,000
3 2,050,000
1 62,000,000
Sieve Size U.S. Mesh Micron Size Aprox. no. of particles per carat (0.2 gm)
16 1190 33
18 1000 57
20 841 97
25 707 160
30 595 282
35 500 460
40 420 770
45 354 1,334
50 297 2,080
60 250 3,240
70 210 6,140
80 177 10,400
100 149 17,140
120 125 20,920
140 105 49,400
170 88 83,400
200 74 140,000
230 63 252,000
270 53 384,000
325 44 660,000
400 37 1,130,000
Micron U.S. Mesh
80-125 270/325
54-80 325/400
40-60 400/500
30-40 500/600
20-40 500/800
20-30 600/800
10-20 1200
8-12 1800
5-10 2200
4-8 3000
2-4 8000
1-2 13000
0-1 60000
0-1/2 100000
Size Avg. no. of Round Stones per carat
F 128
E 106
D 84
C 77
B 70
A 62
1 58
2 50
3 40
4 30
5 25
6 20
7 15
8 11
9 9 1/2
10 7
11 5 2/3
12 4 1/2
13 3 1/2
14 3
15 2 2/3
16 2 1/16
17 1 5/6
18 1 2/3
19 1 1/3

Definitions

Micron powder Diamond powder usually prepared by methods of separation other then sieving
Undersize Particle Any diamond particle smaller than the minimum of any size.
Silver’s Fragile diamond particle of needle or rod like shape.
Shales Diamond particle of thin plate like shape, which when seen through
microscope, appear transparent.
Over Size Those diamonds particles exceeding the maximum permissible size for any specific size range, they might be harmful to performance of the size range involved.
Particle size Particle size determined by diameter of a circumscribed circle.
Size Determined by 1. Circumscribed circle or
2. Mutually agreeable to buyer and seller.
Octahedron A solid eight sided diamond with maximum of six points.
Cube A six sided diamond with parallel sides.
Crystal A Octahedron shaped diamond with flat sides and come to relatively sharp points at their intersection.
Elongated A diamond generally cylindrical in shape
Maacles A triangular shaped diamond with parallel flat sides.
A generally triangular shaped diamond with convex sides.
Round Spherical but with cubic crystalline structure.
Dodecahedron A twelve sided diamond with rounded surfaces having six major & eight minor points.