Mean Particle Diameter
The mean particle diameter of the whole sample is computed by multiplying the weight of the fraction by the respective mean sieve openings, summing these weighted values and dividing by the total weight of material caught on the sieves and pan. The following example for a 12 x 30 mesh sample illustrates the method of calculation.
| Sieve No. | Weight Retained On Sieve (g) | Mean Opening (mm) | Weighted Average |
|---|---|---|---|
| On 12 | 1.5 | 2.03a | 3.0 |
| 16 | 25.1 | 1.44 | 36.1 |
| 20 | 50.2 | 1.02 | 51.2 |
| 30 | 22.5 | 0.72 | 16.2 |
| Pan | 1.1 | 0.00b | 0 |
| 100.4 | 106.5 |
Mean Particle Diameter = 106.5100.4 = 1.061 mm
a. Assuming this material would pass the No. 8 sieve (or generally the next larger sieve in the square root of two series).
b. Material caught on the pan is not considered in calculating the Mean Particle Diameter.