# Porosity and Permeability Calculator

URL: https://speedycalculator.com/calculators/physics/porosity-and-permeability/
Last updated: 2026-10-30

> The porosity and permeability calculator finds the permeability of a core sample from a Darcy flow test (flow rate, viscosity, length, area and pressure drop) and its porosity from the residence time of the fluid.

## Inputs

- Flow rate Q (mL/s, mL/min, m³/s)
- Viscosity μ (mPa·s (cP), Pa·s)
- Sample length L (cm, mm, m, in, ft)
- Cross-section area A (cm², m²)
- Pressure drop ΔP (kPa, Pa, bar, psi, atm, MPa)
- Mean residence time (s, ms, min, h, days)

## Results

- Permeability k
- In m²
- Porosity φ

## Formula

```
k = Q·μ·L/(A·ΔP),  φ = V_pore/V_bulk = Q·t_res/(A·L)
```

## Explanation

Porosity tells how much space a rock or filter has for fluid; permeability tells how easily fluid moves through it. Good oil reservoirs and aquifers need both.

### How to use the Porosity and Permeability Calculator

- **Flow rate Q**
- **Viscosity μ**
- **Sample length L**
- **Cross-section area A**
- **Pressure drop ΔP**
- **Mean residence time**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Enter the measured flow, viscosity, sample length and area, the pressure drop and the mean residence time.

### Inputs explained

FieldWhat to enterFlow rate QUnits: mL/s, mL/min, m³/sViscosity μUnits: mPa·s (cP), Pa·sSample length LUnits: cm, mm, m, in, ftCross-section area AUnits: cm², m²Pressure drop ΔPUnits: kPa, Pa, bar, psi, atm, MPaMean residence timeUnits: s, ms, min, h, days

### What each result means

- **Permeability k** = [Flow rate Q]×[Viscosity μ]×[Sample length L]÷([Cross-section area A]×[Pressure drop ΔP])÷9.869233e-13×1000
- **In m²** = [Flow rate Q]×[Viscosity μ]×[Sample length L]÷([Cross-section area A]×[Pressure drop ΔP])
- **Porosity φ** = [Flow rate Q]×[Mean residence time]÷([Cross-section area A]×[Sample length L])×100

### Example values

How the main result changes when **Flow rate Q** changes and everything else stays at the example values above:

Flow rate Q (mL/s)Permeability k (mD)0.5253.31250.75379.96871506.6251.25633.28121.5759.937521,013.25

## Worked example

Inputs — Flow rate Q: 1 mL/s; Viscosity μ: 1 mPa·s (cP); Sample length L: 5 cm; Cross-section area A: 10 cm²; Pressure drop ΔP: 100 kPa; Mean residence time: 10 s.

Results — **Permeability k = 506.62498 mD**; In m² = 5.0000e-13 m²; Porosity φ = 20 %.

## Key terms

- **Porosity**: Fraction of volume that is pore space.

## FAQ

**Is high porosity always high permeability?**
No – clay is porous but almost impermeable.

**What is a millidarcy?**
1/1000 darcy ≈ 9.87 × 10⁻¹⁶ m².

**What porosity do sandstones have?**
Typically 10–30%.

**What is residence time?**
Average time fluid spends in the sample.


## Sources

- [Fluid Mechanics (F. M. White) – reference text](https://www.mheducation.com/highered/product/fluid-mechanics-white-chul/M9781260258318.html)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)