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Soil Porosity Calculator

Enter the void ratio to get the soil porosity as a percentage.

How it is calculated

The input is the void ratio e = Vv ÷ Vs: the volume of voids divided by the volume of solid grains. It is a plain number with no unit. The tool converts it to porosity n = e ÷ (1 + e) × 100, which is the void volume as a percentage of the total (solids plus voids) volume. Because the denominator is the total volume, porosity can never reach 100% however large e becomes. A void ratio of 0 gives 0%, and a negative void ratio returns no result. The result is rounded to two decimals. To go back the other way, e = n ÷ (1 − n) with n written as a fraction.

Worked example

A soil sample has a void ratio of 0.65, meaning the voids occupy 0.65 units of volume for every 1 unit of solids. Total volume is 1 + 0.65 = 1.65 units. Porosity: 0.65 ÷ 1.65 = 0.3939, and multiplied by 100 the soil porosity is 39.39%. About 39% of the bulk volume is void space, while the remaining 60.61% is solid particles.

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Common mistakes

  • Typing porosity (for example 0.39 or 39) into the void ratio field. The two are different quantities: a porosity of 39% corresponds to a void ratio of about 0.64.
  • Dividing void volume by total volume to get e. The void ratio is voids divided by solids only.
  • Expecting the result to exceed 100% for very loose soils. A void ratio above 1 is possible, but porosity stays below 100%.
  • Entering a percentage for e, such as 65 instead of 0.65, which gives a porosity near 98.5%.
  • Treating porosity as the same thing as permeability. Porosity says how much space exists, not how easily water flows through it.

About this calculator

This calculator finds soil porosity, n = e ⁄ (1 + e), from the void ratio e — the ratio of the volume of voids (air and water-filled space) to the volume of solid particles in a soil sample. Porosity instead expresses that void space as a fraction of the total soil volume, which is why the two related quantities need this simple conversion between them.

Porosity is a fundamental parameter in geotechnical engineering and hydrogeology: it controls how much water a soil can store, how easily fluids flow through it (permeability), and how much a soil layer will compress under load. Engineers obtain e in the laboratory — typically from the soil's dry density and the specific gravity of its solids — then use this formula to report porosity as the percentage geotechnical reports typically require.

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