Pressure Conversions
Pressure
Pressure is a derived SI quantity defined as force applied perpendicularly to a surface per unit area. The SI unit is the pascal (Pa), equal to one newton per square metre (N/m²), named after the French mathematician and physicist Blaise Pascal. In everyday applications, pressure is most commonly encountered in tyre inflation (measured in PSI or bar), blood pressure monitoring (mmHg), weather forecasting (millibar or hPa), and industrial processes where bar and megapascal are standard.
The standard atmosphere (atm) — defined as exactly 101,325 Pa — represents the average atmospheric pressure at sea level and serves as a fundamental reference point in chemistry, scuba diving, and aviation. The bar, equal to 100,000 Pa, is widely used in meteorology and engineering for its convenient proximity to one atmosphere. The torr and millimetre of mercury (mmHg) are historically derived from Evangelista Torricelli's 1643 barometer experiment and remain in clinical use for blood pressure measurement worldwide.
In engineering and materials science, pressure conversion is critical for ensuring safety margins in pressurised systems. A hydraulic press might operate at hundreds of bar, while a car tyre is typically inflated to 2.2–2.5 bar (32–36 PSI). At the extreme end, the deepest point in the ocean — the Challenger Deep at 11,034 m — subjects equipment to pressures exceeding 1,100 bar (110 MPa), more than 1,000 times atmospheric pressure.
Popular Comparisons
| Pa | bar | psi | atm | mmHg | |
|---|---|---|---|---|---|
| Vacuum (perfect) | 0 | 0 | 0 | 0 | 0 |
| Sea level (std) | 101,325 | 1.013 | 14.70 | 1 | 760 |
| Car tyre | 220,000 | 2.2 | 31.9 | 2.17 | 1,650 |
| Scuba tank | 20,000,000 | 200 | 2,901 | 197.4 | 150,000 |
| Deepest ocean | 110,000,000 | 1,100 | 15,954 | 1,086 | 825,000 |
Frequently Asked Questions (FAQ)
How do I convert PSI to bar for tyre pressure?
Divide PSI by 14.5038 to get bar, or multiply bar by 14.5038 to get PSI. For example, a typical car tyre pressure of 32 PSI equals approximately 2.21 bar. A quick mental shortcut: divide PSI by 15 for a close approximation. Use our converter above to get the exact value for your specific tyre pressure.
What is standard atmospheric pressure and why does it matter?
Standard atmospheric pressure is exactly 101,325 pascals (Pa), also expressed as 1 atm, 1.01325 bar, 14.696 PSI, or 760 mmHg. It represents the average air pressure at sea level and serves as the reference point for many scientific, medical, and engineering measurements. Pressure gauges typically show pressure relative to this standard — a tyre gauge reading of 0 PSI means atmospheric pressure, not a perfect vacuum.