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Soil Specific Gravity Calculator

Specific gravity of soil solids (Gs, also called particle density relative to water) is the ratio of the mass of a given volume of soil grains to the mass of the same volume of water.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Weigh your oven-dry soil solids (Ms), then enter it in grams.
  2. Enter the pycnometer + de-aired water mass (Ma) and the pycnometer + soil + water mass (Mb), all in grams.
  3. Optionally enter the temperature correction factor K (from the standard's table for your test temperature) to report Gs referenced to 20 °C; leave it blank for the value at test temperature.

How it works

Specific gravity of soil solids (Gs, also called particle density relative to water) is the ratio of the mass of a given volume of soil grains to the mass of the same volume of water. In the pycnometer (density-bottle) method used by ASTM D854 and AS 1289.3.5, the volume of the solids is measured indirectly by the water they displace: displaced water = Ms + Ma − Mb, where Ms is the oven-dry solids, Ma is the pycnometer full of water only, and Mb is the pycnometer holding the same solids topped up with water to the mark.

The calculator computes Gs = Ms ÷ (Ms + Ma − Mb). Because water density varies slightly with temperature, standards apply a correction factor K (the ratio of water density at the test temperature to water density at 20 °C) so results are comparable: Gs(20 °C) = Gs(test) × K. Enter K to see the corrected value; leaving it blank reports Gs at the test temperature. This is a laboratory-index calculation only — de-airing, calibrated glassware and the full standard procedure govern accuracy.

Worked example

Pycnometer test on a sandy soil. You oven-dry a soil sample and weigh out Ms = 55.00 g of solids. The pycnometer filled with de-aired water weighs Ma = 651.20 g, and the pycnometer with the soil plus water (topped up to the mark) weighs Mb = 685.40 g. Water displaced by the solids = 55.00 + 651.20 − 685.40 = 20.80 g, so Gs = 55.00 ÷ 20.80 = 2.6442. Leaving the temperature correction at 1 gives a specific gravity of about 2.6442 — typical for a quartz-rich sand.

Common mistakes

  • Confusing specific gravity (dimensionless, ~2.6–2.8) with particle density in g/cm³ or kg/m³. Gs is the ratio to water and has no units; multiply Gs by the density of water to get particle density.
  • Using a wet or air-dried sample mass for Ms. The method requires the OVEN-DRY mass of solids, or the displaced-water balance will be wrong.
  • Entering Mb larger than Ma + Ms (or forgetting to top the pycnometer back to the calibration mark), which makes Ms + Ma − Mb non-positive and gives a meaningless result — the calculator flags this instead of returning an impossible value.

Frequently asked questions

What is a typical specific gravity for soil?

Most inorganic mineral soils have Gs between about 2.60 and 2.80 (quartz sands ~2.65, many clays ~2.70). Organic soils, peats and some volcanic soils are lower (often below 2.4), while iron-rich or heavy-mineral soils can exceed 2.9. Values well outside 2.4–2.9 usually signal trapped air, organics, or a reading error.

Do I need the temperature correction factor?

For a quick index value you can leave K blank and report Gs at the test temperature. For results that comply with ASTM D854 / AS 1289.3.5 and are comparable between labs, apply the K value from the standard's table for your measured water temperature so the value is referenced to 20 °C.

Is specific gravity the same as bulk density or dry density?

No. Gs describes only the solid grains (particle density relative to water) and ignores the voids. Bulk and dry density include the pore space between grains, so they are much lower than Gs would suggest. Gs is, however, an input used to compute void ratio, porosity and saturation from other measurements.

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