Pressure Unit Converter

Gauge pressure is measured relative to atmospheric pressure — a gauge reading of 0 means atmospheric pressure. Absolute pressure is measured relative to a perfect vacuum, so absolute pressure = gauge pressure + atmospheric pressure (approximately 101,325 Pa or 14.696 PSI at sea level). Most industrial pressure transmitters measure gauge pressure by default.

It depends on the region and industry. In North America, PSI is the standard. In Europe and Asia, bar is preferred. In scientific work, Pascal (Pa) and its multiples (kPa, MPa) are used as SI standard units. HVAC systems often use inches of water column (inH₂O) for low differential pressures.

This converter uses internationally accepted conversion factors defined by NIST and ISO standards, accurate to at least 7 significant figures. The tool uses 64-bit floating-point arithmetic providing approximately 15-16 significant digits of precision — more than sufficient for any practical engineering application.

1 bar equals exactly 100,000 Pascals, while 1 PSI equals approximately 6,894.757 Pascals. Therefore, 1 bar ≈ 14.5038 PSI, and 1 PSI ≈ 0.0689476 bar. Quick mental approximation: multiply bar by 14.5 to get PSI, or divide PSI by 14.5 to get bar.

Water column units originate from manometer-based pressure measurement, where pressure is indicated by the height of a water column in a U-tube. Different regions adopted different height units — millimeters in metric countries, inches in imperial countries. These units are common in HVAC and low-pressure differential measurements.

Match the output unit to your control system and regional standards. Use bar or kPa for metric installations, PSI for North American plants, and inH₂O or mmH₂O for HVAC or low-pressure applications. Most modern 4-20mA transmitters can be configured to display in any pressure unit.