Den­sity is defined as weight per unit vol­ume at a spe­c­i­fied tem­per­a­ture. Den­sity cups are used for qual­ity con­trol because errors in paint com­po­si­tion will result in dif­fer­ent den­sity read­ings.  Den­sity cups have also been described as liquid pyc­nome­ters.
 
BYK-Gard­ner Den­sity cups use a cylin­dri­cal shape which pro­vides a large open­ing for easy filling, emp­ty­ing, and clean­ing. The tightly fitted stain­less steel cov­ers have an upward slope to a small hole in the cen­ter to allow excess sam­ple mate­rial to be expelled with­out entrap­ping air bub­bles, which increases accu­racy.

ASTM Cup Vol­ume
In North Amer­ica the term "weight per gal­lon" ( wpg ) is used in the coat­ing indus­try. The vol­ume of the weight per gal­lon cup is such that, at a spe­c­i­fied tem­per­a­ture, the numer­i­cal value in grams of water that it can hold is equal to, or ten times greater than, the numer­i­cal value in pounds of water that a gal­lon con­tainer can hold. A US gal­lon of water weighs 8.32 pounds, thus a Reg­u­lar US weight per gal­lon cup holds ten times this amount in vol­ume, 83.2 ml. When tak­ing a mea­sure­ment, the cup and the sam­ple must be brought to the same equilib­rium tem­per­a­ture (usu­ally 25 °C or 77 °F).

ISO Cup Vol­ume
ISO Cups are machined from stain­less steel, using the met­ric sys­tem. The cups hold a defined vol­ume of liquid of 50 or 100 ml. A tol­er­ance of 0.1 % is guar­an­teed. Test­ing is car­ried out in accor­dance with ISO at 23 °C ± 2 °C.

1 ml = 1 cm³; 1 liter = 1000 ml; spe­cific grav­ity of water = 1 g/ml
1000 ml = 0.2646 U.S. gal­lon; 1 U.S. gal­lon = 3.785 liter

Reg­u­lar
US Cup

Impe­rial Cup

Made of cor­ro­sion resis­tant steel

Mid­get Cup
with tare weight

Den­sity Cups

Pro­ce­dure

• Weigh cleaned den­sity cup empty and record weight
• Tem­per den­sity cup and test liquid (Refer to appro­pri­ate test stan­dard for proper tem­per­a­ture) 
• Fill den­sity cup
• Put cover on with­out tilt­ing
• Avoid air bub­bles
• Remove over­flow­ing liquid care­fully with absor­bent cloth
• Weigh filled den­sity cup
• Cal­cu­late den­sity
  

Tare
weight

Den­sity Cups

BYK-Gard­ner offers four dif­fer­ent sized den­sity cups:

• Reg­u­lar US Cup with a vol­ume of 83.2 ml
• Mid­get cup with a vol­ume of 8.32 ml. The Mid­get cup offers a direct con­ver­sion to lbs/gal, elim­i­nat­ing the need for divid­ing the full cup weight by 10.
• Bri­tish Impe­rial Stan­dard size with a vol­ume of 100 ml.
• ISO stan­dard size with a vol­ume of 100 ml and 50 ml.

The ISO cups come with a test cer­tifi­cate or cal­i­bra­tion cer­tifi­cate. The test cer­tifi­cate con­firms that the cup's dimen­sions com­ply with the approved spe­c­i­fi­ca­tions. The cer­tifi­cate is issued by an inde­pen­dent insti­tute, that tests the cup's liquid vol­ume com­pliance.

ISO Den­sity Cups