ConverterHub

Void Ratio Calculator

Find the void ratio and porosity of a soil sample from its void and solid volumes.

How it is calculated

The tool divides the volume of voids by the volume of solids, e = Vv / Vs, and shows it with three decimals. It then converts to porosity with n = e / (1 + e) and shows it as a percentage with two decimals. Both volumes can be in any unit (cm³, m³, litres) as long as they are the same unit, because the ratio cancels it out. The solid volume must be greater than zero and the void volume cannot be negative; otherwise no result is shown. A void volume of zero is accepted and gives e = 0.000. Unlike porosity, void ratio is not capped at 1, so very loose or soft soils can legitimately give values above 1.

Worked example

A soil sample has 45 cm³ of voids and 100 cm³ of solids. Step 1: e = 45 / 100 = 0.45. Step 2: total volume is 145 cm³, so porosity = 0.45 / (1 + 0.45) = 0.3103, about 31 %. The tool prints a void ratio of 0.450 and a porosity of 31.03%.

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Common mistakes

  • Dividing the void volume by the total volume. That gives porosity, not void ratio; here the tool does it for you in the second output.
  • Entering the total sample volume in the solid volume field. The solids volume is the total minus the voids.
  • Mixing units, for example voids in litres and solids in cm³. The ratio is only meaningful if both use the same unit.
  • Expecting void ratio to stay below 1 or to be shown as a percentage. It is a plain ratio and often exceeds 1 for soft clays and peats.

About this calculator

The void ratio (e) of a soil sample is the volume of voids (air and water-filled space between particles) divided by the volume of solids: e = Vv ÷ Vs. It’s closely related to porosity (n), which expresses the same voids as a fraction of total volume instead, via n = e ÷ (1 + e) — the two describe the same physical property from different denominators and are used interchangeably depending on the calculation at hand.

Geotechnical engineers measure void ratio from lab tests on soil samples, often derived from specific gravity, dry unit weight, and moisture content, to assess how compressible or how well-compacted a soil is, since a lower void ratio generally means a denser, stronger soil less prone to settlement under a foundation’s load. It’s a standard input in soil classification, compaction control on construction sites, and settlement calculations for building and pavement foundations.

Both the void ratio and the corresponding porosity are returned from the void and solid volumes of a soil sample.

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