GIFSQ Tools · Module 2 — Food Chemistry & Physicochemical Testing · Tool 30 of 500
Pycnometer method: weigh the empty pycnometer, filled with water, and filled with the sample to get specific gravity and density. AOAC 945.06.
Try sample values — fills the form with the worked example below.
–
Specific gravity
–
Density (g/mL)
–
Water density (g/mL)
Equation: Specific gravity = (msample − mempty) ÷ (mwater − mempty). Density = specific gravity × density of water at the measurement temperature.
Method: AOAC 945.06 (specific gravity by pycnometer). Density of water: 0.9991 g/mL at 15 °C, 0.9982 at 20 °C, 0.9970 at 25 °C, 0.9956 at 30 °C.
Assumptions: the pycnometer is filled to the same mark each time; the sample and the water are at the stated temperature; no air bubbles are trapped.
Limitations: viscous or gassy samples trap air and read low; the result is only as good as the temperature match — a 5 °C drift shifts the water density by about 0.001 g/mL. Hydrometer readings need the same temperature correction.
Rounding: specific gravity and density to 3 decimal places.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: AOAC 945.06 (specific gravity by pycnometer). Density of water: 0.9991 g/mL at 15 °C, 0.9982 at 20 °C, 0.9970 at 25 °C, 0.9956 at 30 °C.
Assumptions: the pycnometer is filled to the same mark each time; the sample and the water are at the stated temperature; no air bubbles are trapped.
Limitations: viscous or gassy samples trap air and read low; the result is only as good as the temperature match — a 5 °C drift shifts the water density by about 0.001 g/mL. Hydrometer readings need the same temperature correction.
Rounding: specific gravity and density to 3 decimal places.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Empty pycnometer 25.000 g, with water 75.000 g, with syrup 79.100 g, at 20 °C. Specific gravity = (79.100 − 25.000) ÷ (75.000 − 25.000) = 54.100 ÷ 50.000 = 1.082; density = 1.082 × 0.9982 = 1.080 g/mL.
Enter values above to see results.
Typical specific gravity: water 1.000, milk 1.028–1.034, orange juice 1.045–1.055, honey 1.38–1.45, vegetable oil 0.91–0.93, ethanol 0.789. A Brix of 20 corresponds to a specific gravity near 1.083. Tool 30 of 500 — GIFSQ
