Enter the masses of a pycnometer test: the oven-dried soil, the pycnometer filled with water, and the pycnometer with the soil and water. The calculator gives the specific gravity of the soil solids, $G_s$ , at the test’s temperature and corrected to 20 °C. It follows ASTM D854, and it’s free and needs no account.

Calculator · ASTM D854

Dry soil

Mass of the empty container

The container's tare, in grams.

Container + dry soil

After oven-drying to constant mass.

Pycnometer

Empty pycnometer

Clean and dry, in grams.

Pycnometer + water

Filled with distilled water at the test's temperature.

Pycnometer + water + soil

With the soil in and the water topped up to the same mark.

Temperature

Test temperature

°C

The standard asks for 20 ± 5 °C. Pick the temperature below and the water's density comes with it.

Water density by temperature

TemperatureDensity

At 20 °C water's density is 0.99821 g/cm³. Click another row to change the test's temperature.

2.691

Specific gravity at 20 °C · Gs = 2.691 at 20 °C

29.6 g (307.8 − 278.2). At 20 °C its density is 0.99821 g/cm³, and at 20 °C 0.99821. 11.02 cm³, the water the soil displaces. Gs = 2.691 at the test's temperature; corrected to 20 °C, Gs₂₀ = 2.691

The test's results

Quantity	Value
Dry soil mass · Ms307.8 − 278.2	29.6g
Water density at the test's temperature · ρ	0.99821g/cm³
Pycnometer volume · V(MBW − MB) / ρ	249.65cm³
Grains' volume · Vg(MBW + Ms − MBWS) / ρ	11.02cm³
Specific gravity at the test's temperature · GsMs / (MBW + Ms − MBWS)	2.691
Specific gravity at 20 °C · Gs₂₀Gs × ρ / ρ₂₀	2.691

This calculator is offered for information and technical support. It doesn't replace professional judgment or the reviews due, and its use is the user's responsibility.

How it calculates

The dry soil’s mass is the container with the dry soil minus the empty container, $M_s = M_{cs} - M_c$ . In the pycnometer, the soil pushes out its own volume of water. The pycnometer with soil and water, $M_{BWS}$ , therefore weighs as much as the pycnometer with water, $M_{BW}$ , plus the soil, minus the water the soil displaced, and that displaced water has the same volume as the grains:

G_{s,T} = \frac{M_s}{M_{BW} + M_s - M_{BWS}}

Both pycnometer weighings are made at the test temperature $T$ , filled to the same mark. ASTM D854 corrects the result to 20 °C with the ratio of the water’s densities:

G_{s,20} = K\,G_{s,T}, \qquad K = \frac{\rho_w(T)}{\rho_w(20\,^\circ\mathrm{C})}

The water’s density comes from a table from 15 to 25 °C, interpolated between whole degrees. The calculator also shows the pycnometer’s volume, $(M_{BW} - M_B)/\rho_w$ , and the volume of the grains, $(M_{BW} + M_s - M_{BWS})/\rho_w$ . It warns when the grains’ volume comes out at zero or less, when $G_{s,20}$ falls outside 2.5 to 2.8, the usual range of mineral soils, and when the temperature is outside the table.

The full procedure, equipment and report are in the Academy lesson: Specific gravity of soil.

How to use it

Under Dry soil, enter the mass of the empty container and of the container with the oven-dried soil.
Under Pycnometer, enter its mass empty, filled with water, and with the soil and water topped up to the same mark.
Enter the test temperature, or pick its row in the Water density by temperature table, and the water’s density comes with it. The standard asks for 20 ± 5 °C.
Read $G_s$ at 20 °C, with $G_s$ at the test temperature and the two volumes in the table.

Restore the example brings back the worked example. The phase relations, hydrometer and Proctor calculators all take $G_s$ as an input.

Frequently asked questions

What is the formula for the specific gravity of soil?

$G_s = M_s/(M_{BW} + M_s - M_{BWS})$ : the mass of the dry soil over the mass of water it displaces in the pycnometer. ASTM D854 then corrects it to 20 °C with $K = \rho_w(T)/\rho_w(20\,^\circ\mathrm{C})$ .

What is a typical specific gravity of soil?

Mineral soils almost always fall between 2.5 and 2.8, and quartz sands sit close to 2.65. Organic matter lowers it, and heavy minerals such as iron oxides can take it above 3.

Why is the specific gravity corrected to 20 °C?

Water gets less dense as it warms, so the same soil gives a slightly different ratio at each temperature. Correcting to 20 °C lets results from different days and labs be compared. The correction is small: between 15 and 25 °C, $K$ stays within about 0.1 % of 1.

Why does the air have to come out of the soil?

Air bubbles trapped in the soil take room the water should fill, so the pycnometer holds less water and the grains seem bigger than they are. That gives a $G_s$ that’s too low, which is why ASTM D854 de-airs the slurry, with vacuum, heat or both, before weighing.

Specific gravity of soil calculator (ASTM D854)