Convert intrinsic permeability between darcy, millidarcy, µm² and m² — used in petroleum and groundwater engineering.
Fluids • 5 units
All 5 units on the Permeability Converter are defined against the Meter² (m²), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 darcy = 1,000 mD. Change either side and every row in the table recalculates with it.
Everything runs in your browser — no account, no uploads, nothing leaves your device.
The darcy sits close enough to the square micrometre to be mistaken for it: one darcy is 0.9869 µm², about 1.3% smaller. That near-equality is convenient and hazardous in equal measure, because a permeability quoted in µm² and one quoted in darcies look almost identical while differing by more than the precision of many measurements. The default step on this page, darcies to millidarcies, is the plain factor of a thousand that reservoir work runs on.
The unit is defined through Darcy's law, which makes flow proportional to permeability and pressure gradient and inversely proportional to fluid viscosity. That viscosity term is why permeability belongs to the rock alone: the same formation passes water, oil and gas at very different rates, and dividing out viscosity is what leaves a property of the solid rather than of the pair. It is also why the same unit describes groundwater aquifers, filter media and concrete durability, disciplines that otherwise share very little vocabulary.
A single permeability figure rarely tells the whole story. Absolute permeability is measured with one fluid saturating the rock; as soon as two phases are present, each flows at some fraction of that value, and those relative permeability curves depend on saturation history rather than on the rock alone. Gas measurements add a further correction, because gas slips along pore walls in a way liquids do not and returns a permeability that is too high until the Klinkenberg correction is applied. Converting the units is the least of the work.
Quick reference — 1 Darcy (darcy) is equal to:
| Meter² | m² | 9.869233e-13 |
| Millidarcy | mD | 1,000 |
| Micrometer² | µm² | 0.9869233 |
| Centimeter² | cm² | 0.0000000099 |
5 units of permeability, each a fixed multiple of the m². The table spans 1,013,249,965,828,145:1, from mD (9.8692e-16 m²) to m² (1 m²). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 m² = 1 m²1 darcy = 9.8692e-13 m²1 mD = 9.8692e-16 m²1 µm² = 1.0000e-12 m²1 cm² = 0.0001 m²where:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 darcy = 25000 mD
This is the fluid-mechanics quantity, not the magnetic one, and its SI unit of square metres (m²) is the giveaway — permeability is an area because it describes the effective cross-section available to flow through a porous solid.
The working unit is the darcy, about 9.869 × 10⁻¹³ m², defined so that a one-darcy rock passes one centipoise fluid at a convenient laboratory rate. Reservoir rock typically runs from a few millidarcies in tight formations to several darcies in clean sandstone, a range of thousands. The same quantity governs groundwater movement, filtration media and the behaviour of concrete, which is why the conversions here cross so many disciplines.