Coarse or fineness of powder is expressed by reference  to the nominal mesh aperture size of the sieve through which powder is able to pass.

Grade of powder as per Indian pharmacopoeia

1.            Coarse powder

2.            Moderately coarse powder

3.            Moderately fine powder

4.            Find powder

A) Coarse Powder:

• A powder, all the particles of which pass through a sieve with nominal mesh aperture of 1.70 mm (Sieve No. 10 ) and not more than 40% pass through nominal mesh aperture of 355 µm (Sieve No. 44) is called a Coarse Powder.

B) Moderately Coarse Powder: 

• A powder, all the particles of which pass through a sieve with nominal mesh aperture of 710 µm (Sieve No. 22) and not more than 40% pass through nominal mesh aperture of 250 µm (Sieve No. 60) is called a Moderately Coarse Powder.

C) Moderately Fine Powder:

• A powder, all the particles of which pass through a sieve with nominal mesh aperture of 355 µm (Sieve No. 44) and not more than 40% pass through nominal mesh aperture of 180 µm (Sieve No. 85) is called a Moderately Fine Powder.

D) Fine Powder: 

• A powder, all the particles of which pass through a sieve with nominal mesh aperture of 180 µm (Sieve No. 85) is called a Fine Powder.

E) Very Fine Powder:

• A powder, all the particles of which pass through a sieve with nominal mesh aperture of 125 µm (Sieve No. 120) is called a Fine Powder.
• Note:
  • For Fine & Very fine grade of powder: IP has prescribed only the upper limit (Fine & Very fine)
  • Fineness of powder is described by means of Number: it indicates that all particles of powder shall pass through that sieve number (respective nominal mesh aperture in µm).