Pressure Converter

Named after Blaise Pascal (1623–1662), French mathematician who proved air has weight via the Puy de Dôme mountain experiment (1648). Formally adopted as an SI unit in 1971 by the General Conference on Weights and Measures.

• Base SI unit for all pressure calculations
• Structural stress and material testing
• Aerodynamics and fluid dynamics
• Sound intensity measurement (micropascals)

• 1 Pa ≈ the pressure of a banknote lying flat on a table
• Standard atmosphere = 101,325 Pa
• Threshold of hearing ≈ 20 µPa (0.00002 Pa)
• Pascal invented the first mechanical calculator at age 18

A practical 1000× SI multiple, adopted widely during global metrication in the 1970s–80s. It replaced older units for tyre pressure, atmospheric reports, and medical readings in Commonwealth nations and Europe.

• Tyre pressure in Australia, Canada, and NZ (220–240 kPa)
• Meteorological weather forecasts
• Blood pressure in some countries (replacing mmHg)
• Food packaging and nitrogen flush pressure

• Standard atmosphere = 101.325 kPa
• Bicycle tyre: 550–700 kPa; car tyre: 220–240 kPa
• Boiling point of water changes ~0.037 °C per kPa near 100 °C
• 1 kPa = 1000 Pa exactly by SI definition

Emerged as an engineering necessity when high-pressure hydraulic and industrial systems became widespread in the 20th century. Gradually replaced kgf/cm² in materials science, structural engineering, and manufacturing standards globally.

• Concrete and structural compressive strength rating
• Hydraulic press and industrial machine pressure
• Tensile and yield strength of metals and polymers
• Aerospace pressure vessel testing

• 1 MPa = 10 bar ≈ 145 PSI
• Regular concrete: 20–40 MPa; high-strength: up to 100 MPa
• Human cortical bone compressive strength ≈ 170 MPa
• Hydraulic car lifts typically operate at 10–20 MPa

Introduced by Norwegian meteorologist Vilhelm Bjerknes in 1909. Derived from the Greek "baros" (weight). Designed to approximate sea-level atmospheric pressure for meteorological convenience. Though not officially SI, it remains accepted across industries worldwide.

• Weather maps and isobar charts
• Scuba and SCBA cylinder pressure (200–300 bar)
• Industrial gas cylinders and hydraulic systems
• Espresso machine extraction pressure

• Perfect espresso is extracted at exactly 9 bar
• Standard atmosphere = 1.01325 bar
• Scuba cylinders hold 200–300 bar — up to 300× atmosphere
• 1 bar = 100,000 Pa exactly by definition

Adopted alongside bar in early 20th-century meteorology. Used on weather maps worldwide for decades until many countries switched to the numerically identical hectopascal (hPa) in the 1980s–90s. The two units are interchangeable: 1 mbar = 1 hPa.

• Meteorological observations and synoptic weather maps
• Aircraft cabin pressure monitoring
• Atmospheric science and climate research
• Altimeter settings in some aviation contexts

• Standard atmosphere = 1013.25 mbar
• 1 mbar = 1 hPa — the same number, different label
• Record low pressure: Typhoon Tip (1979) at 870 mbar
• Cruising altitude pressure (~35,000 ft) ≈ 230 mbar

Rooted in the British imperial system, PSI rose to prominence during the Industrial Revolution as steam boiler technology spread in the 1800s. It remains the primary pressure unit in the United States and is still widely recognised in the UK.

• Tyre pressure in the US and UK (32–35 PSI typical)
• Residential water supply plumbing (40–80 PSI)
• Pneumatic tools and air compressors
• Natural gas pipelines and steam boiler ratings

• Standard atmosphere ≈ 14.696 PSI
• Human bite force ≈ 100–150 PSI; crocodile ≈ 3,700 PSI
• Mariana Trench bottom pressure ≈ 15,750 PSI
• A typical car engine produces cylinder pressure of 150–200 PSI

Historically defined as the average atmospheric pressure at sea level and used as a reference baseline since the 17th century. Precisely fixed at 101,325 Pa in 1954 by the International Committee on Weights and Measures, making it an exact reference rather than a measured value.

• Chemistry standard conditions (STP: 0 °C, 1 atm)
• Scuba diving depth-pressure calculations
• Aviation cabin pressure and altitude reference
• Industrial gas cylinder reference standard

• Every 10 m of ocean depth adds approximately 1 atm
• Mt. Everest summit pressure ≈ 0.337 atm
• Venus surface pressure ≈ 92 atm — like diving 920 m underwater
• Mars atmospheric pressure ≈ 0.006 atm, barely above vacuum

Born from Evangelista Torricelli's mercury barometer (1643) — the first instrument to measure atmospheric pressure. Torricelli observed mercury rising 760 mm in a vacuum tube, defining the unit. The related "Torr" is named in his honour (1 Torr ≈ 1 mmHg).

• Blood pressure measurement — the universal clinical standard
• Intraocular (eye) pressure in ophthalmology
• Vacuum levels in laboratory equipment
• Legacy barometric weather stations

• Normal blood pressure = 120/80 mmHg worldwide
• Standard atmosphere = 760 mmHg (historical definition)
• Healthy eye pressure: 10–21 mmHg; above 21 = glaucoma risk
• Mercury barometers are now banned in many countries due to toxicity

The imperial counterpart to mmHg, inHg emerged in the English-speaking world alongside Torricelli's barometer. It became entrenched in US aviation and meteorology — aircraft altimeters in the United States are still calibrated in inHg to this day.

• Aviation altimeter QNH settings in the US and Canada
• US and Canadian weather forecast pressure reports
• HVAC system static pressure measurement
• Refrigeration and vacuum system ratings

• Standard atmosphere = 29.92 inHg
• US pilots set altimeters to local QNH in inHg before every flight
• Record low for a hurricane: Wilma (2005) at 26.05 inHg
• 1 inHg = 25.4 mmHg = 3,386 Pa exactly

Derived from hydraulic head — the height of a water column that produces a given pressure. Used since Roman aqueduct engineering and formalised with the metric system for pump and pipeline design. Still dominant in civil and mechanical engineering for water systems.

• Water pump head pressure specification
• Water tower and elevated tank design
• Plumbing head-loss calculations
• Irrigation, drainage, and dam engineering

• 10 mH₂O ≈ 1 bar ≈ 1 atm — a handy rule of thumb for divers
• Typical urban water supply: 20–50 mH₂O
• Also written as m WC, mwc, or m col. agua
• Burj Khalifa water supply requires pumps exceeding 800 mH₂O

A "technical metric" unit from the MKS (metre-kilogram-second) system, predating SI. Popular in Germany, Japan, and India before SI adoption. Still found on older pressure gauges, boiler nameplates, and engineering manuals across Asia.

• Boiler and pressure vessel ratings in India and Japan
• Soil and foundation bearing capacity (geotechnical engineering)
• Older tyre pressure gauges in India and Southeast Asia
• Pre-SI industrial compressor and pump documentation

• 1 kg/cm² ≈ 1 bar ≈ 1 atm ≈ 14.22 PSI — the "almost 1" unit
• Many Indian roadside tyre shops still use this unit
• Also written as kgf/cm², AT (technical atmosphere), or just "at"
• Standard atmosphere = 1.0332 kg/cm² — only 3.3% above exactly 1