Determination of specific gravity of milk

Specific gravity:

Specific gravity is the ratio of the density of a substance to the density of a reference substance; relative density.


A lactometer is just like a hydrometer, consisting of a long narrow graduated (10 or 15 to 40; Quevenne scale) glass stem which is enlarged below into a hollow glass bulb weighted with mercury and lead shots. 

Lactometer for Specific gravity of milk test



When a lactometer floats in a milk sample it displaces an amount of milk equal in weight to the weight of the floating lactometer. 


Lactometer, Glass cylinder, and thermometer.


  1. The given sample of milk is thoroughly mixed and brought to a temperature between 50-70°F.
  2. It is then poured into a high glass cylinder by its sides and the lactometer is slowly lowered into the fluid until it floats.  
  3. There it is allowed to remain in position for about half a minute.
  4. The lactometer must float freely without touching the walls of the cylinder or its bottom.
  5. When it becomes stationary records: 
  6. Scale reading &
  7. Temperature
Cyliner for lactometer test


 If the temperature is above or below the standard, (60°F) the lactometer reading is corrected according to the following rule:

  • Add 0.1 to the lactometer reading, or 0.0001 to the specific gravity for every one degree Fahrenheit above the standard temperature.
  • Subtract 0.1 from the lactometer reading or 0.0001 from the specific gravity for every one degree Fahrenheit below the standard temperature. 
  • The specific gravity of the milk is then calculated by following the formula;

                     Specific Gravity of Milk=1+(CLR)/1000 

                     CLR= Corrected lactometer reading


 The lactometer reading for a milk sample of a cow is 31.9 at 63°F, calculating its specific gravity (1.029-1.032).


    CLR          = 63°F – 60°F                 =3

                         = 3 x 0.1                            =0.3

          CLR          = 31.9+0.3                         = 32.2


Specific Gravity   =1+(CLR)/1000 

    SG                   = 1+ 32.2 / 1000

                          = 1+ 0.0322   


Values for specific gravity of different milk:

For Cow’s milk: The value is between 1.026 – 1.032.

For Buffalo milk: The value between 1.030 – 1.034.

For Skim milk: The value is between 1.034 – 1.036.

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