When deciphering fertiliser and mineral particle sizes from analysis reports the following units maybe used.
US Mesh 10 – 2000um – 2mm – 0.0787″
US Mesh 100 – 149um – 0.149mm – 0.0059″
US Mesh 200 – 74um – 0.074mm – 0.0029″
US Mesh 400 – 37um – 0.037mm – 0.0015″
Size Guide Number (SGN)
The SGN figure references the diameter of the “average particle” in millimetres (mm) multiplied by 100. The average particle size of a fertiliser product with an SGN of 300 is 3mm. For SGN300 50% will pass through a 3mm screen and 50% of the particles will be retained on the 3mm screen.
SGN 200 – 2mm
SGN 150 – 1.5mm
SGN 100 – 1mm
UI (Uniformity Index)
The Uniformity Index is a method of determining how consistency of the granule diameter. It compares the particle size at which 95% of the fertiliser/granule is retained on a screen, divided by the particle size at which 10% is retained (and 90% passes through the screen), multiplied by 100. The higher the number (UI), the greater number of particles that are close in size to the SGN. A UI of 100 means all the granules have the same size. A Uniformity Index of 50 means that the average diameter of the small particles is half that of the large particles. A UI of 50 is considered to be good.
