microbar

A microbar, symbolized as μbar (or ubar in ASCII), is a unit of pressure equal to one millionth of a bar. Since 1 bar is defined as exactly 100,000 pascals, 1 μbar equals 0.1 pascal (1 μbar = 0.1 Pa). The pascal is the SI unit of pressure, while the bar and its submultiples are non-SI units.

In practice, the microbar is not commonly used in modern meteorology or most engineering fields, where pressures are typically expressed in pascals, hectopascals (equal to millibars), or atmospheres. Millibars and hectopascals remain common for atmospheric pressure, whereas microbars are more often encountered in older literature or in certain areas of vacuum science.

Conversions and scale: 1 μbar = 0.1 Pa; 10 μbar = 1 Pa; 100 μbar = 10 Pa; 1 bar = 1,000,000 μbar. By extension, 1 atmosphere is about 1.01325 bar, which is roughly 1.01325 × 10^6 μbar. This illustrates how microbars map onto the familiar SI and non-SI pressure scales and why the unit is rarely needed for everyday measurements.

Note: μbar is distinct from microbarn (μb), a unit of area used in particle physics; the former measures pressure, the latter particle cross-sectional area.