Pressure Unit Converter
Pressure is force per unit area. The SI unit is the pascal (Pa), but engineers, meteorologists, clinicians, and physicists all use different units in practice. This converter handles pascals, kilopascals, bar, millibar, standard atmospheres, pounds per square inch (psi), and millimeters of mercury (mmHg). All factors are traceable to the NIST SP 811 exact definitions: 1 atm = 101,325 Pa exactly, 1 bar = 100,000 Pa exactly, and 1 psi = 6,894.757293168 Pa.
Pressure conversion factors (referenced to Pascal)
1 Pa = 0.001 kPa = 0.00001 bar = 0.01 mbar = 9.8692e-6 atm = 0.000145038 psi = 0.0075006 mmHg
The pascal is the SI base unit. All conversions route through Pa: the input is converted to Pa, then divided by each target factor.
Common pressure unit contexts
- Pascal / kPa: Engineering, scientific work, and tire pressure specifications outside North America.
- Bar / mbar: Meteorology, industrial process control, and SCUBA diving equipment.
- atm: Chemistry, gas law calculations, and altitude pressure references.
- psi: North American tire pressure, hydraulic systems, and industrial pressure gauges.
- mmHg: Medical blood pressure, vacuum systems, and laboratory manometry.
Pressure unit converter: frequently asked questions
How many psi is 1 bar?
One bar equals 14.5038 psi. This is derived from the exact definition: 1 bar = 100,000 Pa, and 1 psi = 6,894.757 Pa.
What is the difference between atm and bar?
One standard atmosphere (atm) is exactly 101,325 Pa. One bar is exactly 100,000 Pa. So 1 atm = 1.01325 bar. The bar is more commonly used in meteorology and engineering, while atm appears in chemistry and gas laws.
What is mmHg and how does it relate to Torr?
Millimeters of mercury (mmHg) and Torr are nearly identical: 1 Torr is defined as exactly 1/760 of a standard atmosphere, giving 133.322 Pa. One mmHg equals 133.322 Pa by the same definition for practical purposes.
What pressure unit is used for blood pressure?
Blood pressure is measured in mmHg (millimeters of mercury). A normal reading of 120/80 means 120 mmHg systolic over 80 mmHg diastolic.
What does kPa stand for and when is it used?
kPa stands for kilopascal. One kPa equals 1,000 Pa. It is used for tire pressure in many countries (replacing psi), and for weather pressure in meteorology alongside hPa (hectopascal, equal to 1 millibar).
Official sources
- NIST Special Publication 811: Guide for the Use of the International System of Units (SI).
- BIPM SI Brochure: The International System of Units.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.