Geology & Earth ScienceEarth MaterialsGCSE
AQAIBBrevet (DNB)CambridgeCAPSCBSECCEACISCE

Porosity Calculator

The percentage of void space in a rock or sediment.

Use the free calculatorCheck the variablesOpen the advanced solver
Open Advanced Calculator
This is the free calculator preview. Advanced walkthroughs stay in the app.
Result
Ready
Porosity

Formula first

Overview

Porosity quantifies the empty space within a material, representing the fraction of the total volume that is not occupied by solid particles. In geology, it's crucial for understanding fluid storage and flow in rocks and sediments, making it a fundamental property of aquifers and hydrocarbon reservoirs, and directly influences a material's ability to hold fluids.

Symbols

Variables

\phi = Porosity, V_v = Void Volume, V_t = Total Volume

Porosity
Void Volume
Total Volume

Apply it well

When To Use

When to use: Use this equation when determining the fractional void space within a bulk material sample, such as rock cores, soil samples, or sediment packs. It's particularly useful for unconsolidated materials or porous solids where the void volume can be directly measured or inferred, and assumes V_total is the total bulk volume including both solids and voids.

Why it matters: Porosity directly controls the storage capacity of geological formations for fluids like groundwater, oil, and natural gas, impacting water resource management and energy exploration. It also influences the rate at which fluids can migrate through the subsurface, which is critical for contaminant transport studies and geothermal energy projects.

Avoid these traps

Common Mistakes

  • Forgetting to multiply by 100.
  • Confusing porosity with permeability (flow rate).

One free problem

Practice Problem

A rock sample has a total volume of 250 cm³ and its void spaces account for 75 cm³. Calculate the porosity of this sample.

Total Volume250 cm³
Void Volume75 cm³

Solve for:

Hint: Divide the void volume by the total volume before multiplying by 100 to express as a percentage.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Wikipedia: Porosity (geology)
  2. Earth Science (15th Edition) by Tarbuck, Lutgens, and Tasa
  3. Wikipedia: Porosity
  4. IUPAC Gold Book: Porosity
  5. Bird, R. Byron, Stewart, Warren E., Lightfoot, Edwin N. Transport Phenomena.
  6. Incropera, Frank P., DeWitt, David P., Bergman, Theodore L., Lavine, Adrienne S. Fundamentals of Heat and Mass Transfer.
  7. IUPAC Gold Book, 'porosity'
  8. Wikipedia, 'Porosity'