Physics
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Darcy's Law Calculator.
Calculate porous-media volumetric flow from permeability, area, pressure drop, viscosity, and length.
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Results update automatically as you type.
This page applies only the stated idealized equation and explicit inputs; verify specialized engineering, medical, or safety decisions against applicable standards.
Use Cases
Estimate groundwater flow through an aquifer
Hydrogeologists can use this calculator to estimate the volumetric flow rate of groundwater through a porous medium, given the aquifer's properties and pressure conditions.
Example: Permeability: 1e-12 m², area: 100 m², pressure drop: 1000 Pa, viscosity: 0.001 Pa·s, length: 10 m → flow ≈ 1e-5 m³/s
Design filtration systems
Engineers can calculate the flow rate through filter media to ensure proper sizing and performance, using the media's permeability and system pressure drop.
Example: Permeability: 5e-11 m², area: 0.5 m², pressure drop: 5000 Pa, viscosity: 0.001 Pa·s, length: 0.2 m → flow ≈ 6.25e-5 m³/s
Frequently Asked Questions
- What is Darcy's Law?
- Darcy's Law is an equation that describes the flow of a fluid through a porous medium. It states that the flow rate is proportional to the permeability, cross-sectional area, and pressure drop, and inversely proportional to the fluid's dynamic viscosity and the flow length.
- What units should I use for the inputs?
- Use SI units: permeability in square meters (m²), cross-sectional area in square meters (m²), pressure drop in pascals (Pa), dynamic viscosity in pascal-seconds (Pa·s), and flow length in meters (m). The calculator will output volumetric flow rate in cubic meters per second (m³/s).
- Can this calculator be used for groundwater flow?
- Yes, Darcy's Law is commonly applied to groundwater flow through aquifers. By entering the aquifer's permeability, cross-sectional area, pressure drop (or hydraulic gradient), and fluid viscosity, you can estimate the volumetric flow rate.
Tips & Common Mistakes
Tips
- Ensure all inputs are in SI units to get the correct volumetric flow rate in m³/s.
- Double-check the permeability value; it is often given in darcies or millidarcies, so convert to m² (1 darcy ≈ 9.869233e-13 m²).
- For anisotropic media, use the permeability in the direction of flow.
- Remember that Darcy's Law assumes laminar flow and a homogeneous, saturated porous medium.
Common Mistakes to Avoid
- Using inconsistent units, such as mixing centimeters and meters, which leads to incorrect results.
- Forgetting to convert pressure drop from bars or psi to pascals (1 bar = 100,000 Pa, 1 psi ≈ 6894.76 Pa).
- Assuming the flow length is the total length of the medium, but it should be the distance over which the pressure drop occurs.
Last updated: August 13, 2026