Porosity and Permeability Calculator
Compute porosity from void and bulk volumes, then derive intrinsic permeability in Darcy units from a simple flow experiment — core inputs for reservoir engineering and soil science.
cm³
cm³
mL/s
cP
cm
cm²
atm
Fraction of total volume that is void space
- 1
Porosity φ = Vv ÷ Vt
30 cm³ ÷ 100 cm³ = 0.3 - 2
Porosity (%)
0.3 × 100 = 30 - 3
Permeability k = Q × μ × L ÷ (A × ΔP)
0.05 × 1 × 5 ÷ (10 × 1) = 0.0250 DDarcy units: Q in mL/s, μ in cP, L in cm, A in cm², ΔP in atm
How does this calculator work?
Porosity φ = void volume / total volume. Permeability k (Darcy) = Q × μ × L / (A × ΔP) from a saturated core-plug flow test, with Q in mL/s, μ in centipoise, L and A in cm, ΔP in atm. 1 Darcy ≈ 9.87 × 10⁻¹³ m². Reservoir sandstones typically show 10–30% porosity and 10–500 mD permeability.
Formula
How this is calculated
Porosity φ is the fraction of a rock or soil sample's total volume that consists of void space (pores, fractures, or cavities). It is calculated simply as the void volume divided by the total bulk volume: φ = Vv / Vt. Typical values range from under 5% in crystalline basement rocks to 35–45% in unconsolidated sands; well-cemented sandstone reservoirs are commonly 10–25%. Porosity tells you how much fluid a rock can store, but not how easily that fluid can flow.
Permeability k measures the ease of fluid flow through a connected pore network, governed by Darcy's law: Q = (k × A × ΔP) / (μ × L), where Q is the volumetric flow rate (mL/s), A is the cross-sectional area of the sample (cm²), ΔP is the applied pressure difference (atm), μ is the fluid's dynamic viscosity (centipoise), and L is the sample length (cm). Rearranging gives k in Darcies — a unit defined so that 1 Darcy yields 1 mL/s flow of a 1-cP fluid across 1 cm² under 1 atm/cm. One Darcy equals approximately 9.869 × 10⁻¹³ m² in SI. Tight shale may be 0.001–0.1 millidarcy; productive sandstone reservoirs 10–500 mD; gravel beds can exceed 100 Darcies.
Assumptions: the flow is laminar (low Reynolds number), the fluid is Newtonian and incompressible, and the sample is fully saturated. These conditions hold well for laboratory core-plug tests. High flow rates, gas flow (Klinkenberg effect), or clay swelling can cause deviations from ideal Darcy behaviour.
Frequently asked questions
Productive sandstone reservoirs typically have porosities of 10–30%. Less than 10% is generally considered tight and low-permeability; above 30% is found mainly in shallow, unconsolidated sands. Carbonate reservoirs (limestone, dolomite) often have lower matrix porosity (5–15%) but may be highly fractured.
A conventional oil or gas reservoir typically needs permeability of at least 1–10 mD to produce at commercial rates. High-quality reservoirs exceed 100 mD. Tight gas and shale plays produce from rock with 0.001–1 mD using hydraulic fracturing to create flow paths.
Not necessarily. A rock can have high porosity but very low permeability if the pores are not well connected — for example, vesicular volcanic rock or some chalks. Conversely, a fractured rock can have low matrix porosity but high effective permeability through the fracture network.
Also known as
TG we-Calculate Editorial Team. (2026). Porosity and Permeability Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/porosity-and-permeability-calculator
TG we-Calculate Editorial Team. "Porosity and Permeability Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/porosity-and-permeability-calculator.
TG we-Calculate Editorial Team, "Porosity and Permeability Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/porosity-and-permeability-calculator
@misc{wecalculate_porosity_and_permeability_calculator, title = {Porosity and Permeability Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/porosity-and-permeability-calculator}}, year = {2026}, note = {TG we-Calculate} }
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