Permeability (Porous Media) converter
Intrinsic permeability of rock and porous media, in darcies and their SI equivalent.
Converter
Quick pairs
tap to loadOne millidarcy in every permeability (porous media) unit
7 rows| Unit | Symbol | 1 mD equals |
|---|---|---|
| Square meter | m² | 9.869233e-16 |
| Square centimeter | cm² | 9.869233e-12 |
| Darcy | D | 0.001 |
| Microdarcy | µD | 1,000 |
| Nanodarcy | nD | 1,000,000 |
| Square micrometer | µm² | 0.0009869233 |
| Square foot | ft² | 1.062315e-14 |
How the millidarcy to square meter conversion works
This category is referenced to the square meter (m²), because intrinsic permeability of a porous medium is, physically, an area — roughly the cross-sectional size of the pore pathways a fluid can travel through. The darcy and its sub-multiples (millidarcy, microdarcy, nanodarcy) are the units actually used in practice, each a thousand times smaller than the last, while square centimeter, square micrometer, and square foot give the same area-based quantity in other everyday length scales.
The featured pair is millidarcy to square meter: m² = mD × 9.869233e-16, with the reverse direction multiplying by roughly 1.01325e15.
A moderately productive sandstone reservoir with a permeability of 100 mD converts to 100 × 9.869233e-16 = 9.869233e-14 m². A tight shale formation, by contrast, might measure only 0.01 mD, converting to 0.01 × 9.869233e-16 = 9.869233e-18 m² — four orders of magnitude tighter.
Permeability in darcies is the defining number in oil and gas reservoir engineering, where it determines how easily oil or gas can flow toward a wellbore under a given pressure gradient (Darcy's law), and the same unit shows up in geothermal reservoir assessment, groundwater hydrogeology studies of rock formations, and the characterization of industrial filters and membranes where pore structure needs to be quantified precisely.
The non-round conversion factor (9.869233e-16, not a clean power of ten) traces back to how the darcy was originally defined through Darcy's law itself, tying flow rate, viscosity, pressure gradient, and area together in cgs units rather than being an independently chosen round number — so always carry the full factor rather than approximating it. A second, more consequential confusion is mixing up permeability (an area, measured in m² or darcies) with hydraulic conductivity (a velocity, measured in m/s or similar), a related but distinct quantity used in civil and groundwater engineering; the two are connected through fluid viscosity and density but are not the same unit and should never be substituted for one another.
Questions
How many square meter are in one millidarcy?
One millidarcy equals 9.869233 × 10⁻¹⁶ square meter.
Which units does this permeability converter cover?
Eight units referenced to square meter: square meter, square centimeter, darcy, millidarcy, microdarcy, nanodarcy, square micrometer, and square foot.
Why isn't the darcy-to-square-meter conversion factor a round number?
The darcy was originally defined through Darcy's law itself, combining flow rate, fluid viscosity, pressure gradient, and cross-sectional area in cgs units, so its SI equivalent (9.869233 × 10⁻¹³ m² for a full darcy) inherited that definition's awkward decimal rather than being chosen as a tidy round figure.
When would I use darcy instead of square meter?
Darcy and millidarcy are the near-universal units in petroleum and geothermal reservoir engineering and geology, where typical rock permeabilities fall conveniently in the 0.01 to a few thousand millidarcy range; square meter or square micrometer are more common in materials science and physics, where permeability is derived from first-principles pore-scale models.
Is permeability the same thing as hydraulic conductivity?
No, though the two are often confused. Permeability (measured in m² or darcies) describes the pore structure of the medium itself, independent of the fluid; hydraulic conductivity (measured in m/s or similar) folds in the properties of the specific fluid flowing through it, such as its viscosity and density, so the same rock has one permeability but a different hydraulic conductivity for water versus oil.
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