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Pressure unit conversion

Pressure is defined as force exerted perpendicularly per unit area. In the International System (SI), the fundamental unit is the pascal (Pa), equivalent to one newton per square meter (N/m²). However, in industrial practice multiple metric and imperial units coexist—bar, atmosphere, psi, millimeter of mercury, among others—requiring accurate and validated conversions.

Pressure Unit Conversion Table

Section titled “Pressure Unit Conversion Table”
Unit Symbol Equivalence (Pa and psi)
Pascal Pa 1 Pa / 0,000145038 psi
Kilopascal kPa 1 000 Pa / 0,145038 psi
Bar bar 100 000 Pa / 14,5038 psi
Standard atmosphere atm 101 325 Pa / 14,6959 psi
Technical atmosphere at 98 066,5 Pa / 14,223 psi
Millimeter of mercury (0 °C) mmHg 133,322 Pa / 0,0193368 psi
Inch of mercury (32 °F) inHg 3 386,38 Pa / 0,491154 psi
Kilogram-force per cm² kgf/cm² 98 066,5 Pa / 14,223 psi
Psi (pound per square inch) psi 6 894,76 Pa / 1 psi
Pound per square foot psf 47,8803 Pa / 0,00694444 psi
Inch of water column (4 °C) inH₂O 249,082 Pa / 0,036126 psi
Foot of water column (4 °C) ftH₂O 2 988,98 Pa / 0,433527 psi
Meter of water column (4 °C) mH₂O 9 806,38 Pa / 1,42233 psi
Torr Torr 133,322 Pa / 0,0193368 psi*

*1 Torr equals 1 mmHg.

Conversion Formula

Section titled “Conversion Formula”

p (Pa) = p (unit) × k

Variable Description
p (Pa) pressure value in pascals
p (unit) numerical value in the source unit
k conversion factor from source unit to Pa

Direct Conversion Factors

Section titled “Direct Conversion Factors”

Conversion of the most common units to pascals.

Source Unit Conversion Factor to Pa and Equivalence
bar ×100 000 (1 bar = 100 kPa / 14,5 psi)
atm ×101 325 (1 atm = 101,325 kPa / 14,696 psi)
psi ×6 894,76 (1 psi ≈ 6,895 kPa / 1 psi)
mmHg ×133,322 (1 mmHg = 0,133 kPa / 0,0193 psi)
inHg (32 °F) ×3 386,38 (1 inHg = 3,386 kPa / 0,491 psi)
kgf/cm² ×98 066,5 (1 kgf/cm² = 98,07 kPa / 14,22 psi)
inH₂O (4 °C) ×249,082 (1 inH₂O = 0,249 kPa / 0,0361 psi)

Inverse Conversion Factors

Section titled “Inverse Conversion Factors”

Conversion from pascals to the most common units (inverse k = 1 / direct k).

Desired Unit Conversion Factor from Pa and Equivalence
bar ×0,00001 (1 Pa = 1×10⁻⁵ bar / 1,45×10⁻⁷ psi)
atm ×9,86923×10⁻⁶ (1 Pa = 9,87×10⁻⁶ atm / 1,43×10⁻⁹ psi)
psi ×0,000145038 (1 Pa ≈ 1,45×10⁻⁴ psi)
mmHg ×0,00750062 (1 Pa = 0,0075 mmHg / 1,09×10⁻⁶ psi)
inHg (32 °F) ×0,0002953 (1 Pa = 2,953×10⁻⁴ inHg / 4,28×10⁻⁵ psi)
kgf/cm² ×1,01972×10⁻⁵ (1 Pa = 1,02×10⁻⁵ kgf/cm² / 1,48×10⁻⁶ psi)
inH₂O (4 °C) ×0,0040147 (1 Pa = 4,01×10⁻³ inH₂O / 5,82×10⁻⁴ psi)

Notes on Accuracy and Special Cases

Section titled “Notes on Accuracy and Special Cases”

The conversion factors presented assume standard gravity conditions (gₙ = 9,80665 m/s²) and reference temperature where applicable. In the case of liquid columns (Hg, H₂O), fluid density and temperature affect the result:

  • Mercury: the standard conversion uses 0 °C for mmHg (density 13 595,1 kg/m³) and 32 °F for inHg. Some sectors use inHg at 60 °F (1 inHg⁶⁰°F = 3 376,85 Pa), introducing a difference of ≈0,3 % from the value at 32 °F.
  • Water: is normally referenced at 4 °C (maximum density). For HVAC applications at 60 °F, 1 inH₂O ≈ 248,84 Pa.
  • Standard atmosphere vs. technical atmosphere: the standard atmosphere (atm) equals 101 325 Pa, while the technical atmosphere (at) is defined as 1 kgf/cm² = 98 066,5 Pa, therefore 1 atm ≈ 1,0332 at.
  • Torr and mmHg: in practice, 1 Torr = 1 mmHg = 133,322 368 Pa, although historically small differences existed.
  • Conversions involving kilogram-force (kgf) or pound-force (lbf) assume standard gravitational acceleration, so they must be used with caution under different local gravity conditions.
  • For high-accuracy engineering calculations, it is recommended not to round intermediate factors; the values listed here maintain at least five significant figures to minimize cumulative errors.

Sources Consulted

Section titled “Sources Consulted”