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Old 06-14-2006, 01:18 PM
John
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Default Re: Conversion of Mesh to mm.

Particle Size Conversion
Sieve Designation Nominal Sieve Opening
Standard Mesh inches mm Microns
25.4 mm 1 in. 1.00 25.4 25400
22.6 mm 7/8 in. 0.875 22.6 22600
19.0 mm 3/4 in. 0.750 19.0 19000
16.0 mm 5/8 in. 0.625 16.0 16000
13.5 mm 0.530 in. 0.530 13.5 13500
12.7 mm 1/2 in. 0.500 12.7 12700
11.2 mm 7/16 in. 0.438 11.2 11200
9.51 mm 3/8 in. 0.375 9.51 9510
8.00 mm 5/16 in. 0.312 8.00 8000
6.73 mm 0.265 in. 0.265 6.73 6730
6.35 mm 1/4 in. 0.250 6.35 6350
5.66mm No.3 1/2 0.223 5.66 5660
4.76 mm No. 4 0.187 4.76 4760
4.00 mm No. 5 0.157 4.00 4000
3.36 mm No. 6 0.132 3.36 3360
2.83 mm No. 7 0.111 2.83 2830
2.38 mm No. 8 0.0937 2.38 2380
2.00 mm No. 10 0.0787 2.00 2000
1.68 mm No. 12 0.0661 1.68 1680
1.41 mm No. 14 0.0555 1.41 1410
1.19 mm No. 16 0.0469 1.19 1190
1.00 mm No. 18 0.0394 1.00 1000
841 mm No. 20 0.0331 0.841 841
707 mm No. 25 0.0278 0.707 707
595 mm No. 30 0.0234 0.595 595
500 mm No. 35 0.0197 0.500 500
420 mm No. 40 0.0165 0.420 420
354 mm No. 45 0.0139 0.354 354
297 mm No. 50 0.0117 0.297 297
250 mm No. 60 0.0098 0.250 250
210 mm No. 70 0.0083 0.210 210
177 mm No. 80 0.0070 0.177 177
149 mm No. 100 0.0059 0.149 149
125 mm No. 120 0.0049 0.125 125
105 mm No. 140 0.0041 0.105 105
88 mm No. 170 0.0035 0.088 88
74 mm No. 200 0.0029 0.074 74
63 mm No. 230 0.0025 0.063 63
53 mm No. 270 0.0021 0.053 53
44 mm No. 325 0.0017 0.044 44
37 mm No. 400 0.0015 0.037 37
Larger sieve openings (1 in. to 1/4 in.) have been designated by a sieve "mesh" size that corresponds to the size of the opening in inches. Smaller sieve "mesh" sizes of 3 1/2 to 400 are designated by the number of openings per linear inch in the sieve.

The following convention is used to characterize particle size by mesh designation:

a "+" before the sieve mesh indicates the particles are retained by the sieve;
a "-" before the sieve mesh indicates the particles pass through the sieve;
typically 90% or more of the particles will lie within the indicated range.
For example, if the particle size of a material is described as -4 +40 mesh, then 90% or more of the material will pass through a 4-mesh sieve (particles smaller than 4.76 mm) and be retained by a 40-mesh sieve (particles larger than 0.420 mm). If a material is described as -40 mesh, then 90% or more of the material will pass through a 40-mesh sieve (particles smaller than 0.420 mm).

This information is also provided on page T848 of the Aldrich 2003-2004 Catalog/Handbook of Fine Chemicals.
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