micropascals

Micropascals are a unit of pressure in the International System of Units (SI). The symbol is μPa, and the prefix micro denotes 10^-6, so 1 μPa equals 10^-6 pascals. Consequently, 1 Pa equals 1,000,000 μPa and 1 MPa equals 1,000,000,000,000 μPa. The micropascal is used for measuring very small pressure changes where higher units would be impractical or misleading.

Because μPa represent extremely small pressures, their use is concentrated in specialized applications such as ultra-sensitive vacuum measurements, calibration of high-precision pressure sensors, and certain acoustic measurements where pressure fluctuations are described relative to the standard reference of 20 μPa for human hearing. In acoustics the sound pressure level is commonly expressed in decibels relative to 20 μPa (dB re 20 μPa).

Common context and scale help illustrate the magnitude: the threshold of human hearing at typical frequencies is about 20 μPa, while atmospheric pressure is about 1.013 × 10^11 μPa. In practice, engineers may report pressures in μPa for low-level measurements or convert to Pa, kPa, or MPa as needed.

Notation can vary: μPa is standard, but 'uPa' is sometimes used in plain ASCII environments where the micro symbol is unavailable. Related units include the microbar (μbar), where 1 μbar equals 0.1 Pa or 1 × 10^5 μPa.