Pressure Converter

Free Online Pressure Converter — PSI, Bar, Pascal, mmHg, Atm and More

Pressure is force distributed over an area, and it is measured in more different units across more different technical fields than almost any other physical quantity. A mechanical engineer checks hydraulic system pressure in PSI. A meteorologist monitors atmospheric pressure in millibars or hectopascals. A chemist describes gas pressures in atmospheres or kilopascals. A medical professional measures blood pressure in millimeters of mercury (mmHg). A European tire inflation label specifies pressure in bar. Our free online pressure converter handles all of these unit families, delivering instant conversions across the full range of scientific, engineering, and everyday pressure measurement contexts.

The Pascal — SI Pressure Unit from Atmospheric to Microscopic Scales

The pascal (Pa) is the SI unit of pressure, defined as one newton of force per square meter (1 Pa = 1 N/m²). It is named for Blaise Pascal, the 17th-century French mathematician and physicist who made fundamental contributions to fluid mechanics and atmospheric pressure measurement. The pascal is the base unit for pressure in all SI-compliant scientific and engineering calculations, and it scales through the standard SI prefix system to accommodate the enormous range of pressures encountered in nature and technology.

One pascal is an extremely small pressure — atmospheric pressure at sea level is approximately 101,325 pascals. For most engineering applications, kilopascals (kPa, 1,000 Pa) and megapascals (MPa, 1,000,000 Pa) are more practical scales. Tire pressure is typically 200-250 kPa (gauge). Hydraulic system pressures in industrial machinery commonly reach 20-35 MPa. High-pressure water jet cutting systems operate at 400-600 MPa. Diamond synthesis requires pressures exceeding 6,000 MPa (6 GPa). The Earth's core experiences pressures exceeding 300 GPa. The pascal scale accommodates all of these extremes through its prefix system.

In meteorology, pressure is most commonly expressed in hectopascals (hPa, 100 Pa each), which are numerically identical to millibars — a historical unit that remains in common use alongside hPa in weather reporting. Standard sea-level atmospheric pressure is 1013.25 hPa (or 1013.25 mbar). Weather maps use isobars (lines of equal pressure) labeled in hPa to show high-pressure and low-pressure systems. A barometric pressure of 1020 hPa indicates fair, stable weather, while a rapid drop to 990 hPa or below signals an approaching storm system.

PSI — Pounds per Square Inch in American Industry

Pounds per square inch (PSI) is the dominant pressure unit in the United States for most engineering and consumer applications. Tire pressure, hydraulic system pressure, compressed air system pressure, natural gas pipeline pressure, and fluid power specifications are all expressed in PSI in the American market. One PSI equals approximately 6,894.76 pascals (6.895 kPa), and standard atmospheric pressure equals 14.696 PSI.

Tire pressure is the most common PSI application in everyday consumer life. Passenger car tires are typically inflated to 32-35 PSI, truck tires to 80-120 PSI, and bicycle tires to 80-130 PSI depending on tire width and riding style. Tire pressure is always expressed as gauge pressure — the pressure above ambient atmospheric pressure — not absolute pressure. A tire at 32 PSI gauge contains air at an absolute pressure of approximately 32 + 14.7 = 46.7 PSI. When converting tire pressure to bar for a European vehicle specification (or vice versa), both values are gauge pressures, so the conversion is direct: 32 PSI ≈ 2.21 bar.

Hydraulic system engineering in the US uses PSI for all pressure specifications. Typical industrial hydraulic systems operate at 1,000-3,000 PSI, while high-performance systems can reach 5,000-10,000 PSI. Converting these values to MPa for comparison with European hydraulic components (which typically use MPa or bar) is a routine need in international industrial procurement. 1,000 PSI ≈ 6.895 MPa ≈ 68.95 bar — all of these represent the same pressure in different units.

Bar — The European and Scientific Standard

The bar is a unit of pressure defined as exactly 100,000 pascals (100 kPa), making it approximately equal to average atmospheric pressure at sea level (which is 101,325 Pa = 1.01325 bar). The bar is not an SI unit in the strict sense, but it is accepted for use with SI units and is widely used in European engineering, the petroleum industry, and scientific applications where pressures near atmospheric are described.

The millibar (mbar, 100 Pa) is particularly important in meteorology — it is numerically identical to the hectopascal (hPa) that appears on modern weather maps and barometers. European vehicle tire specifications express pressure in bar, and European pneumatic tool and compressor specifications use bar as standard. Converting between bar and PSI is one of the most frequent practical pressure conversions: 1 bar ≈ 14.5038 PSI, or approximately 14.5 PSI per bar as a quick mental approximation.

Atmospheres — Reference Pressure in Chemistry and Physics

The standard atmosphere (atm) is a unit defined as exactly 101,325 pascals, approximately equal to the average atmospheric pressure at sea level at latitude 45°. It is used extensively in chemistry, physics, and materials science as a convenient reference pressure for specifying standard conditions under which thermodynamic properties and chemical reactions are measured and tabulated.

Standard temperature and pressure (STP) — 0°C and 1 atm — and standard conditions (25°C and 1 bar) are reference states used throughout chemistry for reporting standard enthalpy, entropy, and Gibbs free energy values. Gas solubility in liquids (Henry's Law), gas volume calculations using the ideal gas law, and phase diagram analysis all reference pressure in atmospheres when using textbook values. Converting experimental measurements from instrument-native units (often kPa or PSI) to atmospheres for comparison with tabulated standard values is a routine laboratory need.

mmHg and Torr — Medical and Vacuum Measurement

The millimeter of mercury (mmHg) is the unit used universally for blood pressure measurement and in some clinical contexts for measuring intraocular pressure (eye pressure). One mmHg equals 133.322 pascals and derives from the physical setup of a mercury manometer: the pressure that supports a column of mercury exactly one millimeter tall. Standard atmospheric pressure equals exactly 760 mmHg.

The torr, named for Italian physicist Evangelista Torricelli who invented the mercury barometer, is defined as 1/760 of a standard atmosphere. For practical purposes, 1 torr ≈ 1 mmHg (they differ by less than 0.000014%). The two units are used interchangeably in most contexts, with mmHg preferred in medical settings and torr more common in vacuum technology and physics.

Vacuum levels are described in torr or millibars: a "medium vacuum" of 1-10 torr, a "high vacuum" of 10⁻³ to 10⁻⁶ torr for electron microscopes and semiconductor processes, and an "ultra-high vacuum" below 10⁻⁹ torr for particle accelerators and surface science experiments. Understanding these pressure scales and converting between them is essential for vacuum system engineering, where pressure specifications from different equipment manufacturers must be reconciled into consistent operational parameters.