Atmospheric Pressure, inches of Mercury, and Pascals

I got a smart watch for Christmas. It has a ‘compass’ that also shows my longitude, latitude, altitude, and the Atmospheric Pressure in hPA.

So I studied up on the units for Atmospheric Pressure. Disclaimer: This is crude. I want to get some numbers I can remember.

Pa is an SI unit for atmospheric pressure. It means Pascal. One Pascal is 1 Newton per square meter. hPa is hectopascal. 1 hPa = 100 Pa

The ‘Imperial’ (English) unit would be PSI (pounds per square inch). BTW, 1 PSI is quite a bit, but 1 Pascal isn’t much.

Often the weather person on television give the atmospheric pressure in inches of Mercury (inHg).


1 inHg = 33.9 hPa
.02953 inHg = 1 hPa

Low, Regular, and High Pressure

1000 hPa (29.5 inHg) is low pressure.
1010 hPa (29.8 inHg) is ‘regular’ pressure.
1040 hPa (30.7 inHg) is high pressure.

The key is which direction is the barometric pressure going (rising or decreasing).

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