Darcy’s Law Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Fluid calculations are especially sensitive to density, viscosity, geometry, pressure conventions, and unit systems. Darcy’s Law Calculator narrows that problem to the relationship used on this page, making the displayed darcy flow rate easier to audit against the inputs and the governing equation.

What this calculator does

The Darcy’s Law Calculator uses Permeability (k) to estimate the page’s Darcy flow rate from the fluid-mechanics relationship below. It is meant for a defined geometry and property set, so the useful part is not just the headline number but also whether your density, viscosity, dimensions, pressure reference, and flow convention match the model.

How to use it

Start with the fields that actually drive this result: Permeability (k). Keep units consistent with the menus beside the fields and avoid mixing values measured under different conditions. After calculating, change one input at a time if you are comparing scenarios; that makes cause-and-effect much easier to see.

How the calculation works

For laminar porous-media flow, Darcy’s law is Q = kAΔp/(μL). The relationship can also be rearranged for permeability, pressure difference, or another compatible quantity when the necessary values are available.

Example

For k = 1×10⁻¹² m², A = 0.01 m², Δp = 100,000 Pa, μ = 0.001 Pa·s, and L = 0.1 m, Darcy’s law gives Q = 1×10⁻⁵ m³/s. If the page’s filled inlet/outlet defaults do not reproduce an expected nonzero Δp, enter/check the pressure-difference path explicitly and verify the result by hand.

How to interpret the result

Interpret the Darcy flow rate within the fluid, geometry, pressure reference, and property values you entered. A numerically plausible answer can still be physically wrong if gauge/absolute pressure, diameter/radius, viscosity type, or unit convention is mismatched, so compare the result with the assumptions as well as the formula.

Limitations and notes

The present page can fail to reflect its filled inlet/outlet pressure defaults in the headline, so verify Δp explicitly and cross-check Q = kAΔp/(μL). Darcy’s law also assumes an appropriate porous-medium regime and consistent intrinsic-permeability units.