Pressure Conversion Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
To convert a pressure, it's brought back to a common unit (the pascal) then converted into the new unit. For example, 1 atmosphere represents about 1.013 bar, or about 14.7 psi.
Explanation
Several pressure units coexist depending on the field: the pascal (Pa) is the International System unit, the bar is commonly used in meteorology and for tire pressure in Europe, the psi (pound-force per square inch) remains the standard in the United States for tire pressure and plumbing, and the millimeter of mercury (mmHg) is still used in medicine (blood pressure) and meteorology. The standard atmosphere (atm), defined exactly as 101,325 Pa, serves as a historical reference close to average atmospheric pressure at sea level. All the constants used here are exact definitions (not rounded measured values), which guarantees an accurate conversion in both directions. For a temperature conversion, see our temperature conversion calculator.
Example: converting 1 atmosphere to bars
Inputs
Value: 1. Starting unit: atmosphere. Target unit: bar.
Calculation
1 atm × 101,325 Pa per atm = 101,325 Pa. Dividing by 100,000 (the bar factor) gives 1.01325 bar.
Result
1 atmosphere represents about 1.01325 bar.
Frequently asked questions
What's the difference between bar and atmosphere?
The two are very close (1 atm = 1.01325 bar) but not identical: the bar is a round unit defined at exactly 100,000 Pa, while the standard atmosphere (101,325 Pa) is historically defined from average atmospheric pressure at sea level. The gap between the two (about 1.3%) is generally negligible in everyday use but real.
Why is psi still used for tire pressure in the United States?
Since the United States has never officially adopted the metric system for everyday use, psi (pound-force per square inch) remains the reference unit for tire pressure, plumbing, and many American technical applications, in place of the bar used in Europe.
Is mmHg still a valid scientific unit?
The millimeter of mercury is no longer an International System unit, but it remains widely used in medicine (blood pressure measurement) and meteorology by historical habit. Its exact value (133.322387415 Pa) is defined by convention from the density of mercury and standard gravitational acceleration.