Pressure Conversion: Converting Between Force per Area Units
Pressure conversion transforms measurements of force per unit area from one unit to another. Common units include pascals (Pa), bars, atmospheres (atm), pounds per square inch (psi), and millimeters of mercury (mmHg). Pressure is fundamental in weather forecasting, engineering, medicine (blood pressure), diving, and tire inflation. Different industries use different units by convention, making conversions essential. Understanding pressure conversions helps you interpret weather reports, check tire pressure, understand diving tables, and work with engineering specifications across different standards.
Examples
Pressure Conversion Example
Let's explore pressure conversions with practical examples. Your car's tire placard says 35 psi, but your new gauge shows kPa. Converting: 35 psi × 6.895 = 241.3 kPa. Many gauges show both units now.
A weather report says barometric pressure is 1013 millibars—is that high or low? Standard atmospheric pressure is 1013.25 mbar (or hPa), so this is normal. In the US, you might see 29.92 inches of mercury (inHg) instead—same pressure, different unit.
Blood pressure is measured in mmHg (millimeters of mercury). Normal is about 120/80 mmHg. In other units: 120 mmHg = 0.158 atm = 2.32 psi = 16 kPa. Medicine uses mmHg by convention.
For scuba diving, pressure increases by about 1 atm per 10 meters of depth. At 30 meters: 3 atm gauge + 1 atm surface = 4 atm absolute = 58.8 psi = 405 kPa. Dive tables use these pressures for decompression calculations.
Key conversions to remember: 1 atm ≈ 14.7 psi ≈ 101 kPa ≈ 760 mmHg ≈ 1.01 bar. Understanding these helps you work with pressure across different applications and regions.
Key properties
Pascal: The SI Unit
The pascal (Pa) is the SI unit of pressure, equal to one newton per square meter (N/m²). It's a small unit—atmospheric pressure is about 101,325 Pa. Kilopascals (kPa) and megapascals (MPa) are more practical for everyday use. Understanding pascals is essential for scientific work.
Bar and Atmosphere
1 bar = 100,000 Pa, approximately equal to atmospheric pressure. 1 atm (standard atmosphere) = 101,325 Pa. These units are convenient for everyday pressures. Weather reports often use millibars (mbar = hPa). Understanding bar and atm helps with weather and general applications.
PSI: Pounds per Square Inch
PSI is common in the US for tire pressure, hydraulics, and compressed gas. 1 psi = 6894.76 Pa. Standard atmospheric pressure is 14.7 psi. Car tires typically run 30-35 psi. Understanding psi is essential for US automotive and industrial applications.
mmHg and Torr: Medical Pressure
Millimeters of mercury (mmHg) and torr (1 torr ≈ 1 mmHg) are used in medicine for blood pressure. Normal blood pressure is about 120/80 mmHg. 1 atm = 760 mmHg. Understanding mmHg is essential for medical applications.
Absolute vs. Gauge Pressure
Absolute pressure is measured from zero (vacuum). Gauge pressure is measured from atmospheric pressure. Tire pressure is gauge: 32 psi gauge = 32 + 14.7 = 46.7 psi absolute. Understanding this distinction prevents confusion in pressure readings.
Water and Mercury Columns
Pressure can be expressed as fluid column height: inches of water (inH₂O), feet of water (ftH₂O), or inches of mercury (inHg). These relate pressure to the height of liquid that would be supported. Understanding column units helps with HVAC and manometer readings.
Formulas
PSI to Pascals
Pa = psi × 6894.76
Multiply psi by 6894.76 to get pascals. For example, 30 psi = 206,843 Pa ≈ 207 kPa.
Bar to PSI
psi = bar × 14.504
Multiply bar by 14.504 to get psi. For example, 2 bar = 29 psi.
Atmospheres to mmHg
mmHg = atm × 760
Multiply atmospheres by 760 to get mmHg. 1 atm = 760 mmHg by definition.
kPa to PSI
psi = kPa × 0.145
Multiply kilopascals by 0.145 to get psi. For example, 220 kPa = 31.9 psi.
Pressure Conversions in Science and Industry
Pressure conversions are used across many fields: automotive (tire pressure in psi or kPa), weather forecasting (millibars or inches of mercury), medicine (blood pressure in mmHg), diving (atmospheres for decompression tables), HVAC (inches of water for duct pressure), and engineering (various units depending on region and industry). Understanding pressure conversions helps professionals and individuals work safely and effectively with pressure measurements.
Frequently asked questions
Which pressure units are included?
Pascals, kilopascals, megapascals, bar, millibar, atm, psi, mmHg, torr, inHg, inH₂O, and more.
How do I convert psi to kPa?
Multiply psi by 6.895. For example, 32 psi = 220.6 kPa. We show both directions instantly.
What's the difference between bar and atm?
1 bar = 100,000 Pa, 1 atm = 101,325 Pa. They're close but not identical. 1 atm ≈ 1.013 bar.
Why do tires use different units?
US uses psi, most other countries use kPa or bar. We convert between all tire pressure units.
What about blood pressure units?
Blood pressure uses mmHg (millimeters of mercury). 120/80 mmHg is considered normal. We convert to other units.
How do weather pressure units work?
Weather uses millibars (mbar), hectopascals (hPa), or inches of mercury (inHg). 1 mbar = 1 hPa.
What's absolute vs. gauge pressure?
Gauge measures from atmospheric; absolute from vacuum. Add 14.7 psi (or 101.3 kPa) to convert gauge to absolute.
Can I convert diving pressures?
Yes—water depth to pressure and vice versa. Every 10m depth adds about 1 atm of pressure.
What about vacuum measurements?
Vacuum is measured as pressure below atmospheric. We support negative gauge pressures and torr for vacuum.
How precise are conversions?
We use standard conversion factors. You can set decimal precision for reporting.
What units do hydraulic systems use?
Hydraulics typically use psi (US) or bar/MPa (metric). We convert between all hydraulic pressure units.
Can I convert pressure to force?
Pressure × area = force. Enter pressure and area, and we calculate the resulting force.
What about head pressure?
Fluid column height × density × gravity = pressure. We convert feet/meters of water to pressure units.
How do altitude and pressure relate?
Pressure decreases with altitude. We can estimate pressure at different elevations.
Can I export conversion tables?
Download reference tables showing common pressure unit conversions.