The millipascal is a unit of pressure equal to one thousandth of a pascal. Its symbol is mPa. The pascal is already a very small unit — it is the pressure of a sheet of paper lying on a table — so a thousandth of one is smaller than almost any pressure a person encounters. It survives because two fields genuinely work at that scale: acoustics and viscosity.
Sound is a pressure wave, and the pressures involved are tiny. Ordinary conversation at a metre carries a sound pressure of about 20 millipascals. A whisper is nearer 2, and the threshold of hearing, the quietest sound a healthy young ear can detect, is 0.02 millipascals, which is 20 micropascals. A loud rock concert reaches a few pascals. The entire useful range of human hearing therefore lives between a hundredth of a millipascal and a few thousand of them.
That is why sound is reported in decibels rather than in pressure units. A range spanning a factor of a million is unwieldy in linear numbers, so acoustics takes the logarithm and anchors it at the threshold of hearing. But the decibel is not a unit of pressure at all: behind every decibel figure is a pressure in pascals or millipascals, and instrument calibration is done in those real units.
The second use is stranger, because it is not a pressure at all. Dynamic viscosity is measured in pascal seconds, and almost every liquid people care about lands in the millipascal second range. Water at room temperature is 1 mPa·s exactly enough for practical purposes. That happens to equal one centipoise in the older CGS system, so the switch to SI left every viscosity table numerically unchanged, which is why the millipascal second took hold where the millipascal alone did not.
With that scale in hand, the numbers become legible. Petrol is about 0.6 mPa·s, olive oil about 80, honey several thousand, and glycerol around 1,400. Blood plasma is about 1.3, and whole blood nearer 4, which is one reason blood flow is harder to model than water flow.
For pressure itself, outside acoustics, the millipascal appears in vacuum work and in the gentlest of laboratory measurements — the pressure differences that drive slow gas flow, or the residual pressure in a chamber that has been pumped down hard. In those settings the alternative units are the micropascal below and the pascal above.
One millipascal equals 0.001 pascals, one thousand micropascals, 0.00001 millibars, or about 0.000000145 pounds per square inch.
| Unit | Symbol | 1 Millipascal equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Nanopascal | nPa | 1000000 nPa | 0.000001 mPa | Millipascals to Nanopascals |
| Micropascal | µPa | 1000 µPa | 0.001 mPa | Millipascals to Micropascals |
| Centipascal | cPa | 0.1 cPa | 10 mPa | Millipascals to Centipascals |
| Decipascal | dPa | 0.01 dPa | 100 mPa | Millipascals to Decipascals |
| Pascal | Pa | 0.001 Pa | 1000 mPa | Millipascals to Pascals |
| Newton per square meter | N/m² | 0.001 N/m² | 1000 mPa | Millipascals to Newtons per square meter |
| Decapascal | daPa | 0.0001 daPa | 10000 mPa | Millipascals to Decapascals |
| Hectopascal | hPa | 0.00001 hPa | 100000 mPa | Millipascals to Hectopascals |
| Kilopascal | kPa | 0.000001 kPa | 1000000 mPa | Millipascals to Kilopascals |
| Bar | bar | 0.00000001 bar | 100000000 mPa | Millipascals to Bars |
| Megapascal | MPa | 0.000000001 MPa | 1000000000 mPa | Millipascals to Megapascals |
| Gigapascal | GPa | 1 × 10-12 GPa | 1000000000000 mPa | Millipascals to Gigapascals |
| Terapascal | TPa | 1 × 10-15 TPa | 1 × 1015 mPa | Millipascals to Terapascals |
| Atmosphere | atm | 0.00000000986923266716 atm | 101325000 mPa | Millipascals to Atmospheres |
| Pound per square inch | psi | 0.00000014503773773 psi | 6894757.29317 mPa | Millipascals to Pounds per square inch |
| Kilopound per square inch | ksi | 1.45037743897 × 10-10 ksi | 6894757000 mPa | Millipascals to Kilopounds per square inch |
| Megapound per square inch | Mpsi | 1.45037743897 × 10-13 Mpsi | 6894757000000 mPa | Millipascals to Megapounds per square inch |