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Overview
Pressure (mechanical stress) can be expressed in many units.
Basic Mode: Use the most common units—Pa, atm, bar, psi, torr, mmHg.
Advanced Mode: Also includes technical atmospheres (at), barye, cmHg, cmH₂O, ftHg, ftH₂O, inHg, inH₂O,
kgf/mm², kip per sq in (ksi), pound per sq ft (psf), poundal per sq ft, long‐ton and short‐ton per sq ft, mmH₂O, μmHg, piéze (pź), etc.
Standard definitions:
- 1 Pa = 1 N/m²
- 1 atm = 101 325 Pa
- 1 bar = 100 000 Pa
- 1 psi = 6 894.757 Pa
- 1 Torr = 133.322 Pa
- 1 mmHg = 133.322 Pa
Formula & Methodology
To convert from “Unit A” → “Unit B”, we first convert A → Pascal (Pa), then Pa → B.
Each unit has a known factor “unit_to_Pa.”
Algorithm:
1) Multiply input by unit_to_Pa[fromUnit] → value in Pa.
2) Divide that Pa by unit_to_Pa[toUnit] → result in target unit.
Conversion Table (Unit → Pascal):
| Unit | Symbol | Factor (→ Pa) | Definition / Note |
|---|---|---|---|
| Pascal | Pa | 1 | SI base |
| Atmosphere (standard) | atm | 101325 | 1 atm = 101 325 Pa |
| Bar | bar | 100000 | 1 bar = 100 000 Pa |
| Pound per square inch | psi | 6894.757 | 1 psi = 6 894.757 Pa |
| Torr | torr | 133.322 | 1 torr = 133.322 Pa |
| Millimetre of mercury | mmHg | 133.322 | 1 mmHg = 133.322 Pa |
| Atmosphere (technical) | at | 98066.5 | 1 at ≈ 98 066.5 Pa |
| Barye (CGS unit) | barye | 0.1 | 1 barye = 0.1 Pa |
| Centimetre of mercury | cmHg | 1333.22 | 1 cmHg = 10 mmHg = 1333.22 Pa |
| Centimetre of water (4 °C) | cmH₂O | 98.0665 | 1 cmH₂O = 9.80665 Pa per mmH₂O × 10 |
| Foot of mercury | ftHg | 40636.7 | 1 ftHg = 12 inHg = 12 × 3386.389 Pa ≈ 40636.7 Pa |
| Foot of water (39.2 °F) | ftH₂O | 2989.07 | 1 ftH₂O ≈ 2989.07 Pa |
| Inch of mercury | inHg | 3386.389 | 1 inHg = 3386.389 Pa |
| Inch of water (39.2 °F) | inH₂O | 249.0889 | 1 inH₂O ≈ 249.0889 Pa |
| Kilogram‐force per square millimetre | kgf/mm² | 9806650 | 1 kgf/mm² = 9.80665×10⁶ Pa |
| Kip per square inch | ksi | 6894757.29 | 1 ksi = 1000 psi = 6.89475729×10⁶ Pa |
| Pound per square foot | psf | 47.8803 | 1 psf = 47.8803 Pa |
| Poundal per square foot | pdl/ft² | 1.48816 | 1 pdl/ft² = 1.48816 Pa |
| Long ton per square foot | tnf/ft² | 107992.86 | 1 long ton/ft² ≈ 1.0799286×10⁵ Pa |
| Short ton per square foot | ton_s/ft² | 95396.21 | 1 short ton/ft² ≈ 9.539621×10⁴ Pa |
| Millimetre of water | mmH₂O | 9.80665 | 1 mmH₂O = 9.80665 Pa |
| Micrometre of mercury | μmHg | 0.133322 | 1 μmHg = 0.001 mmHg = 0.133322 Pa |
| Pièze (MTS unit) | pź | 1000 | 1 pièze = 1000 Pa |
Examples
-
Convert 1 atm to psi:
1 atm = 101 325 Pa → ÷ 6894.757 ≈ 14.6959 psi -
Convert 750 mmHg to bar:
750 × 133.322 Pa = 99 991.5 Pa → ÷ 100 000 ≈ 0.9999 bar -
Convert 2 psi to mmH₂O (Advanced):
2 × 6894.757 Pa = 13 789.514 Pa → ÷ 9.80665 ≈ 1406.20 mmH₂O -
Convert 500 cmH₂O to inHg (Advanced):
500 × 98.0665 Pa = 49 033.25 Pa → ÷ 3386.389 ≈ 14.48 inHg -
Convert 10 kgf/mm² to atm (Advanced):
10 × 9 806 650 Pa = 98 066 500 Pa → ÷ 101 325 ≈ 968.93 atm
Frequently Asked Questions
What is the difference between standard atm and technical atm?
Standard atm (atm) is defined as exactly 101 325 Pa. Technical atm (at) is 98 066.5 Pa (often used in engineering).
How does mmHg relate to torr?
1 mmHg is defined as the pressure of a 1 mm column of mercury at 0 °C, equal to 133.322 Pa. 1 torr is defined as exactly 1/760 atm = 101 325 Pa/760 ≈ 133.322 Pa. They are effectively the same.
Why use Pascals (Pa) as the base unit?
Pascal is the SI unit (1 N/m²). Converting all units to Pa ensures consistency and minimizes errors.
How do I convert psi to bar?
Multiply psi by 0.0689476. For example, 10 psi × 0.0689476 ≈ 0.689476 bar.
What is a barye (Ba)?
A barye is a CGS unit of pressure: 1 Ba = 10⁻¹ Pa. Rarely used in modern practice.
What is a piéze (pź)?
A piéze (or pièze) is a metric unit equal to 1000 Pa. It was part of the MTS system.