Pressure Conversion Converter
Convert pressure conversion between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
Formula
Target = Value x (Source-to-Pa factor) / (Target-to-Pa factor)
All conversions go through pascals as the common base unit. First multiply the input value by its unit factor to get pascals, then divide by the target unit factor. For example, 1 atm = 1 x 101325 Pa, then to PSI: 101325 / 6894.76 = 14.696 PSI.
Frequently Asked Questions
What are the most common pressure units and how do they relate?
The most common pressure units are pascal (Pa), bar, atmosphere (atm), PSI, torr, and mmHg. One standard atmosphere equals 101,325 Pa, 1.01325 bar, 14.696 PSI, 760 torr, and 760 mmHg. The pascal is the SI unit (1 N/m2), while bar is popular in European industrial settings. PSI dominates in American engineering. Torr and mmHg are used in vacuum science and medicine respectively. Each unit emerged from different fields, which is why so many coexist in modern use.
Why are there so many different pressure units?
Different pressure units developed independently across various fields and countries. The pascal came from the SI system in 1971. The atmosphere was defined by the pressure at sea level. The torr originated from mercury barometer measurements in the 1600s. PSI developed from the imperial system used in America and Britain. The bar was created as a convenient metric unit close to atmospheric pressure. Each field adopted the unit most convenient for its typical pressure ranges, and legacy usage keeps them all in active use today.
What is gauge pressure versus absolute pressure?
Absolute pressure measures from a perfect vacuum (zero point), while gauge pressure measures relative to the local atmospheric pressure. At sea level, atmospheric pressure is about 101.325 kPa (14.696 PSI), so a tire gauge reading 32 PSI (gauge) actually means 46.7 PSI absolute. Gauge pressure can be negative (vacuum), while absolute pressure is always positive. Units are sometimes suffixed with \"a\" for absolute (psia) or \"g\" for gauge (psig). Scientific calculations typically require absolute pressure.
How do I choose the right pressure unit for my application?
Use pascals or kilopascals for scientific work and international standards. Use bar for European industrial applications and meteorology (as hectopascals). Use PSI for American automotive, HVAC, and industrial applications. Use torr or millitorr for vacuum science and semiconductor manufacturing. Use mmHg for blood pressure and medical applications. Use atmospheres for chemistry and diving calculations. When in doubt, the pascal is always correct as the SI unit, and any other unit can be derived from it.
What are the most common unit conversion mistakes?
Common errors include confusing fluid ounces with weight ounces, mixing up miles and nautical miles, forgetting that UK and US gallons differ (UK is 20% larger), using the wrong temperature formula, and not accounting for the difference between troy and avoirdupois ounces.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.