Enter a cylindrical specimen’s size, its mass before and after oven-drying, and the specific gravity of its grains. The calculator splits the specimen’s volume into solids, water and air, and from that split works out the void ratio, the porosity and the degree of saturation, with the densities and volumes of the test. It’s free and needs no account.

Calculator · ASTM D2216 · D7263

Specimen geometry

Specimen diameter

The mold is a cylinder: the volume comes from its size.

Specimen height

With the diameter, it closes the cylinder's volume.

The test's masses

Container mass

The tare: it comes off the other two masses.

Container + wet specimen

The mass before drying.

Container + dry specimen

The mass after oven-drying.

Solids and water

Specific gravity of the grains

From the specific gravity test; without it the diagram doesn't close.

Water density at the test's temperature

g/cm³

At 20 °C it's 0.998 g/cm³. Measure the temperature and use the table's value.

Phase diagram

Solids64.0 %
Water25.3 %
Air10.8 %

Total volume 200.1 cm³Voids 72.1 cm³

S = 70.1 % · e = 0.563 · n = 36.0 %

A 4.95 × 10.4 cm specimen: wet volume 200.1 cm³. Wet mass 377.2 g, dry 326.7 g and water 50.5 g (water content 15.5 %). With Gs = 2.554 the grains take 128.1 cm³, so the voids take 72.1 cm³. Water fills 70.1 % of the voids: 29.9 % is left to take before it's saturated

The test's thirteen quantities

Quantity	Value
Wet volume · Vπ (D/2)² H	200.1cm³
Wet mass · MMtc − Mc	377.2g
Dry mass · MsMdc − Mc	326.7g
Water mass · MwMtc − Mdc	50.5g
Sample density · γM / V	1.885g/cm³
Water content · wMw / Ms	15.46%
Dry density · γdγ / (1 + w)	1.632g/cm³
Solids volume · VsMs / (Gs · ρw)	128.1cm³
Voids volume · VvV − Vs	72.1cm³
Void ratio · en / (1 − n)	0.563
Porosity · nVv / V	36.01%
Water volume · VwMw / ρw	50.6cm³
Degree of saturation · SrVw / Vv	70.1%

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 specimen is a cylinder, so its volume comes from its diameter $D$ and height $H$ . The container’s mass, $M_c$ , comes off the two weighings, wet ( $M_{tc}$ ) and after oven-drying ( $M_{dc}$ ):

V = \pi \left(\frac{D}{2}\right)^2 H, \qquad M = M_{tc} - M_c, \qquad M_s = M_{dc} - M_c

The water is the difference between the two weighings, $M_w = M_{tc} - M_{dc}$ , and with it come the density, the water content and the dry density:

\rho = \frac{M}{V}, \qquad w = \frac{M_w}{M_s}, \qquad \rho_d = \frac{\rho}{1 + w}

The specific gravity of the grains, $G_s$ , closes the phase diagram: it turns the dry mass into the volume of the solids, and the rest of the specimen is voids.

V_s = \frac{M_s}{G_s\,\rho_w}, \qquad V_v = V - V_s, \qquad n = \frac{V_v}{V}, \qquad e = \frac{n}{1 - n}

Written this way, the void ratio is the same as $V_v/V_s$ . The water fills $V_w = M_w/\rho_w$ of the voids, which gives the degree of saturation:

S = \frac{V_w}{V_v}

$\rho_w$ is the density of water at the test’s temperature. The water content is the oven-drying one of ASTM D2216, and taking the density from a specimen’s measured size is Method A of ASTM D7263. When the data give a saturation over 100 %, no room left for voids, or a dry density above the wet one, the calculator puts a warning over the result and says which datum to check.

The full procedure, equipment and report are in the Academy lesson: Soil phase relations.

How to use it

Measure the specimen’s diameter and height, in cm.
Weigh the empty container, the container with the wet specimen, and the container with the specimen after oven-drying, in grams.
Enter the specific gravity of the grains, from your own test or the specific gravity calculator, and the density of water at the test’s temperature: 0.998 g/cm³ at 20 °C.
Read the phase diagram, which shows the share of the volume taken by solids, water and air. Under it, a table lists the thirteen quantities of the test with their formulas.

The calculator opens with a worked example, and Restore the example brings it back once you’ve changed the data.

Frequently asked questions

How do you calculate the degree of saturation of a soil?

Divide the volume of water by the volume of voids: $S = V_w/V_v$ . If you already know the water content and the void ratio, $S = w\,G_s/e$ gives the same number.

What is the difference between void ratio and porosity?

Both measure the voids. The void ratio compares them with the volume of the solids, $e = V_v/V_s$ , and the porosity with the whole volume, $n = V_v/V$ , so $n = e/(1 + e)$ . Porosity is always under 1, while the void ratio of a soft clay or an organic soil can be well over 1.

Can the degree of saturation be more than 100 %?

No. Water can fill every void and no more, so a result over 100 % is an error in the data, most often in the dry mass, the specimen’s volume or a $G_s$ that’s too low. The calculator flags it.

Why does the calculation need the specific gravity?

The weighings give the mass of the grains and of the water, but not the room the grains take up. $G_s$ turns the dry mass into the volume of the solids, and without that volume there’s no void ratio, porosity or saturation.

Void ratio and degree of saturation calculator