Porosity and Permeability Calculator

Porosity and permeability describe different aspects of a porous material. Porosity is the fraction of bulk volume occupied by void space. It is calculated as φ = Vvoid / Vtotal and displayed here as a percentage. A rock can have high porosity yet poor connectivity between pores, so porosity alone does not determine how readily a fluid can move through it. Accurate volume measurements should use the same unit because only their ratio matters. Intrinsic permeability measures the ability of the connected pore network to transmit fluid independent of the particular fluid used. For one-dimensional steady flow, Darcy's law can be rearranged to k = QμL / (AΔP), where Q is volumetric flow rate, μ is dynamic viscosity, L is sample length, A is cross-sectional area, and ΔP is the pressure difference across the sample. With SI inputs, k is returned in square metres. The calculator also converts to darcies using one darcy equal to 9.869233 × 10⁻¹³ square metres. Darcy's law assumes laminar, viscous-dominated flow through a saturated homogeneous sample. Flow rate and pressure difference should be measured after steady conditions are established. The pressure difference should exclude tubing and fixture losses where possible, while area must be perpendicular to flow and length measured along the flow path. Gas experiments may require compressibility and slip corrections. Multiphase systems require relative permeability rather than the single-phase intrinsic value calculated here. Porosity measurements vary with method. Total porosity includes isolated voids, whereas effective porosity includes only interconnected pore space that contributes to transport. Grain-volume methods, saturation methods, imaging, and mercury intrusion can produce different values because they access different pore sizes. Likewise, permeability can vary by direction in layered or fractured media. A single scalar result may not represent anisotropic material behavior. This calculator is useful for petroleum engineering, hydrogeology, soil science, filtration, ceramics, and laboratory core analysis. It directly applies measured Darcy-flow data rather than estimating permeability solely from grain size. Use calibrated instruments, control temperature because viscosity changes with temperature, and repeat tests at several pressure gradients to verify a linear flow response. Reservoir and geotechnical decisions should also account for stress, saturation, heterogeneity, scale, and applicable test standards.