Pressure Units

International System of Units (SI)

Pressure P is the physical value of the force F acting per unit area of the surface S directed perpendicular to this surface. Thus the pressure formula is P = F / S.

In the international system of units (SI), the pressure is measured in the Pascals (Pa):.
  1 Pa = 1 Newton / 1 square meter (1 N / m²)

For practical measurements in metrology and automation, 1 Pa often turns out to be too small a pressure value, and multipliers (kilo, Mega) multiplying the values by a thousand and a million times respectively, are used to operate the real data.
  1 MPa = 1000 kPa = 1000000 Pa
  Also, scale devices for measuring pressure may be directly calibrated in terms Newton / meter, or derivatives thereof:
  Kilonewton, Meganewton / m², cm², mm².

Then we obtain the following:
  1 MPa = 1 MN/m² = 1 N/mm² = 100 N/cm² = 1000 kN/m² = 1000 kPa = 1000000 N/m² = 1000000 Pa

In many countries, bar and kgf/m² units and their derivatives (mbar, kgf/cm²) are also widely used for measuring pressure.
  1 bar is a non-SI metric unit equal to 100000 Pa.
  1 kgf/cm² is a pressure unit in the gravitational metric system and is widely used in industrial pressure measurements.
  1 kgf/cm² = 10000 kgf/m² = 0.980665 bar = 98066.5 Pa

Atmosphere

The atmosphere is a non-SI metric unit of pressure measurement, approximately equal to the atmospheric pressure of the Earth at the level of the World Ocean.
  There are two concepts of the atmosphere for measuring pressure:

• The physical atmosphere (atm) is equal to the mercury column pressure of 760 mm high at 0° C. 1 atm = 101325 Pa
• The technical atmosphere (at) is equal to the pressure produced by a force of 1 kgf on an area of 1 cm². 1 at = 98066.5 Pa = 1 kgf/cm²

Water column

The meter of the water column (mH₂O) is a non-SI metric unit of pressure measurement used in a number of industries.
  Physically, it is equal to the pressure of a column of water 1 m high at a temperature of 4° C and a standard acceleration of gravity of 9,80665 m/sec².

Derivative units are cmH₂O and mmH₂O
  1 mH₂O = 100 cmH₂O = 1000 mmH₂O
  Relates to other pressure units as follows:
  1 mH₂O = 1000 kgf/m² = 0.0980665 bar = 9.80665 Pa = 73.55592400691 mmHg.

Mercury column

A millimeter of mercury (mmHg) is a non-SI metric unit of pressure measurement, equal to 133.3223684 Pa. The synonym is Torr.
  It is used in a number of technical fields.
  Ratio to water column: 1 mmHg = 13.595098063 mmH₂O.

Imperial and Customary units

Other pressure units are also used in the United States and Britain.

• Inch water column
    Symbol: inH₂O = 249.08891 Pa.
• Foot water column
    Symbol: ftH₂O = 2989.006692 Pa.
• Inch of mercury
    Symbol: inHg = 3386.38815789474 Pa.
• Pound per square inch
    Symbol: psi = 6894.757293178 Pa.
• 1000 pound per square inch
    Symbol: ksi = 6894757.2931783 Pa.
• Pound per square foot
    Symbol: psf = 47.8802589803 Pa.
• American (short) ton per square inch
    Symbol: tsi = 13789514.58633672267344 Pa.
• American (short) ton per square foot
    Symbol: tsf = 95760.51796067168523226 Pa.
• British (long) ton per square inch
    Symbol: br.tsi = 15444256.3366971 Pa.
• British (long) ton per square foot
    Symbol: br.tsf = 107251.780115952 Pa.

Instruments for measuring pressure

Pressure gauges, differential pressure gauges (pressure difference), vacuum gauges (vacuum measurement) are used for pressure measurement.