Pressure Converter

Convert Pressure Units Online — Pascal, Bar, ATM, PSI, and mmHg

Our free pressure converter lets you instantly switch between pascals, bars, atmospheres, pounds per square inch, and millimeters of mercury with precision. Whether you need a quick psi to bar calculation for tire pressure, want to interpret a barometric reading, or are working through engineering problems involving fluid pressure, this tool delivers accurate results in real time. All conversions run entirely in your browser with no data sent to any server and no sign-up required.

How to Convert Between Pressure Units

Pressure conversion relies on fixed ratios between units, all of which can be traced back to the pascal, the SI unit of pressure. Below are the essential formulas, step-by-step examples, and practical notes for the most commonly needed pressure conversions.

PSI to Bar

The formula is bar = psi × 0.0689476. One pound per square inch equals approximately 0.0689476 bar. For example, a typical car tire pressure of 32 psi converts to 32 × 0.0689476 = 2.206 bar. In Europe and most of the world, tire pressure is displayed in bar, while the United States uses psi. A quick mental shortcut for psi to bar conversion is to divide by 14.5 — for instance, 29 psi ÷ 14.5 = 2.0 bar (exact value: 1.999 bar). This approximation works well for everyday tire pressure checks.

Bar to PSI

The formula is psi = bar × 14.5038. Since one bar equals 14.5038 psi, you multiply the bar value by this factor. For example, if a European tire gauge reads 2.4 bar, that equals 2.4 × 14.5038 = 34.81 psi. Industrial compressed air systems often operate at 6 to 8 bar, which equals approximately 87 to 116 psi. When renting a car abroad, knowing this conversion helps you use unfamiliar tire pressure gauges confidently.

ATM to PSI and Bar

The formulas are psi = atm × 14.696 and bar = atm × 1.01325. One standard atmosphere is defined as exactly 101,325 pascals, which equals 14.696 psi or 1.01325 bar. Standard atmospheric pressure at sea level is 1 atm. For example, a scuba diving tank pressurized to 200 atm contains air at 200 × 14.696 = 2939.2 psi or 200 × 1.01325 = 202.65 bar. The atmosphere unit is commonly used in chemistry for gas law calculations and in diving for depth-pressure relationships.

Pascal to Bar and ATM

The formulas are bar = Pa ÷ 100,000 and atm = Pa ÷ 101,325. The pascal is the SI unit of pressure, defined as one newton per square meter. Because the pascal is a very small unit, kilopascals (kPa) and megapascals (MPa) are more commonly used in practice. For example, standard atmospheric pressure is 101,325 Pa = 101.325 kPa = 0.101325 MPa. Tire pressure of 220 kPa equals 220,000 Pa ÷ 100,000 = 2.2 bar. If you work with force calculations related to pressure, our force unit converter can help with newton and pound-force conversions.

mmHg to Other Pressure Units

The formulas are atm = mmHg ÷ 760 and psi = mmHg × 0.0193368. One standard atmosphere equals exactly 760 mmHg (millimeters of mercury). The mmHg unit, also called torr, is widely used in medicine for blood pressure readings and in meteorology for barometric pressure. Normal blood pressure is approximately 120/80 mmHg, meaning the systolic pressure is 120 mmHg (about 2.32 psi or 0.158 atm) and the diastolic pressure is 80 mmHg (about 1.55 psi or 0.105 atm). Mercury barometers, invented by Evangelista Torricelli in 1643, directly measure atmospheric pressure as the height of a mercury column.

About the Pressure Converter

Pressure measurement plays a critical role in engineering, meteorology, medicine, automotive maintenance, diving, and countless industrial processes. Different fields and regions use different pressure units, making conversion an everyday task for professionals and enthusiasts alike. This converter supports all major pressure units and delivers instant, precise results for any input value.

Understanding Pressure and Its Measurement

Pressure is defined as force applied per unit area. The SI unit is the pascal (Pa), named after French mathematician and physicist Blaise Pascal, who made pioneering contributions to fluid mechanics and hydrostatics in the 17th century. Pascal demonstrated that atmospheric pressure decreases with altitude and that pressure applied to a confined fluid is transmitted equally in all directions — a principle now known as Pascal's law, which forms the basis of hydraulic systems used in car brakes, construction equipment, and manufacturing presses.

The bar was introduced by Norwegian meteorologist Vilhelm Bjerknes in 1909 as a convenient unit for atmospheric pressure. One bar equals exactly 100,000 pascals, which is very close to standard atmospheric pressure (101,325 Pa). This near-equivalence makes bar a practical unit for many applications. The millibar (mbar), equal to one hectopascal (hPa), is the standard unit for weather maps and aviation meteorology worldwide. When you hear a weather forecaster mention a pressure of 1013 millibars, that is approximately one standard atmosphere.

The pound per square inch (psi) is rooted in the imperial measurement system and remains dominant in the United States and in certain global industries. Tire pressure, hydraulic system ratings, compressed gas cylinders, and water pressure in plumbing are commonly expressed in psi in North America. The unit is intuitive in the imperial system because it directly relates pounds of force to square inches of area.

The atmosphere (atm) was originally defined as the pressure exerted by a 760-millimeter column of mercury at sea level and 0°C. It serves as a convenient reference point in chemistry, particularly for gas law calculations involving standard temperature and pressure (STP). Scuba divers also use atmospheres to express underwater pressure — every 10.06 meters (33 feet) of seawater depth adds approximately one atmosphere of pressure.

Common Pressure Conversions in Daily Life

Tire pressure is the most frequent reason everyday people need a pressure converter. In the United States, tire pressure is measured in psi — a typical passenger car tire requires 30 to 35 psi. In Europe, Asia, and most other regions, tire pressure is displayed in bar or kilopascals. A sticker inside the driver's door jamb lists the recommended pressure, but if you are using a gauge calibrated in a different unit, you need to convert. For example, 32 psi equals 2.21 bar or 220.6 kPa. Our dedicated psi to bar converter page is designed specifically for this common scenario.

Meteorology relies on pressure measurements to forecast weather. Barometric pressure at sea level averages about 1013.25 hPa (millibars), 29.92 inches of mercury, or 760 mmHg. High pressure systems (above 1020 hPa) generally bring clear skies, while low pressure systems (below 1000 hPa) often indicate storms. Hurricane central pressures can drop below 900 hPa — Hurricane Wilma in 2005 recorded 882 hPa, the lowest Atlantic hurricane pressure on record. Weather stations report pressure in hPa or millibars internationally, while the United States also uses inches of mercury for public forecasts.

Medical applications use mmHg as the standard unit for blood pressure measurement. A healthy adult blood pressure reading is approximately 120/80 mmHg, where 120 is the systolic pressure (heart contracting) and 80 is the diastolic pressure (heart relaxing). Hypertension is diagnosed when readings consistently exceed 140/90 mmHg. Intracranial pressure, intraocular pressure, and central venous pressure are also measured in mmHg in clinical settings. Understanding the relationship between mmHg and other pressure units helps medical professionals communicate across disciplines. For temperature monitoring alongside pressure in medical and scientific contexts, our temperature unit converter is a useful companion tool.

Engineering and industrial applications span a wide range of pressure units and magnitudes. Hydraulic systems in construction equipment operate at 200 to 350 bar (2900 to 5075 psi). Water supply systems typically deliver water at 3 to 5 bar (43.5 to 72.5 psi). Steam boilers in power plants operate at pressures ranging from 10 bar for small industrial boilers to over 300 bar for supercritical power plants. Vacuum systems used in semiconductor manufacturing operate at pressures far below atmospheric — sometimes as low as 10⁻⁹ pascal. For calculations involving the relationship between force and area in pressure problems, our length unit converter can help with area-related dimensional conversions.

Tips and Quick Reference

For a quick psi to bar estimate, remember that 14.5 psi is approximately 1 bar. So you can divide the psi value by 14.5 for a fast mental conversion. For example, 35 psi ÷ 14.5 is roughly 2.4 bar (exact: 2.413 bar). Going the other direction, multiply bar by 14.5 to get psi. This approximation is accurate to within about 0.3 percent, which is more than sufficient for tire pressure checks.

A common mistake is confusing gauge pressure with absolute pressure. Gauge pressure measures pressure relative to atmospheric pressure, while absolute pressure includes atmospheric pressure. A tire gauge reading of 32 psi means 32 psi above atmospheric pressure; the absolute pressure inside the tire is about 32 + 14.7 = 46.7 psi absolute. In engineering notation, psig denotes gauge pressure and psia denotes absolute pressure. Most everyday pressure measurements (tires, water pipes, compressed air) use gauge pressure.

When working with the ideal gas law (PV = nRT), always use absolute pressure in pascals or atmospheres. Using gauge pressure in gas law calculations will produce incorrect results because the equation requires the total pressure acting on the gas, not just the pressure above atmospheric. Similarly, when calculating pressure at depth underwater, remember to add atmospheric pressure: total pressure = atmospheric pressure + (fluid density × gravity × depth).

For medical blood pressure readings, remember that normal is around 120/80 mmHg, elevated is 120-129 systolic with less than 80 diastolic, and high blood pressure stage 1 begins at 130/80 mmHg. These thresholds were updated by the American Heart Association in 2017. Converting 120 mmHg to other units: 120 mmHg = 2.32 psi = 0.158 atm = 16.0 kPa = 0.160 bar.

Common Pressure Conversion Reference Values

The following table lists frequently searched pressure equivalents across Pa, bar, atm, psi, and mmHg. These values are useful for quick lookups and sanity-checking your conversions in automotive, meteorological, medical, and engineering contexts.

Description	Pascal (Pa)	Bar	ATM	PSI	mmHg
Standard atmosphere	101,325	1.01325	1.000	14.696	760.0
Car tire (low)	206,843	2.068	2.041	30.0	1551.3
Car tire (typical)	227,527	2.275	2.245	33.0	1706.4
Bicycle tire (road)	689,476	6.895	6.804	100.0	5171.5
Scuba tank	20,684,300	206.84	204.1	3000	155,132
Blood pressure (systolic)	16,000	0.160	0.158	2.32	120.0
Blood pressure (diastolic)	10,666	0.107	0.105	1.55	80.0
Water at 10 m depth	199,325	1.993	1.967	28.91	1495.0
Industrial hydraulic	20,000,000	200.0	197.4	2900.8	150,012

Frequently Asked Questions

What is the correct tire pressure in bar and psi?

Most passenger car tires require 30 to 35 psi (2.07 to 2.41 bar). The exact recommended pressure is printed on a sticker inside the driver's door jamb or in the vehicle owner's manual. SUVs and trucks may require 35 to 45 psi (2.41 to 3.10 bar). Bicycle tires vary widely — road bikes typically need 80 to 130 psi (5.5 to 9.0 bar), while mountain bike tires run at 25 to 50 psi (1.7 to 3.4 bar). Always check pressure when tires are cold, as driving heats the air inside and temporarily increases the reading by 3 to 5 psi.

What is the difference between gauge pressure and absolute pressure?

Gauge pressure measures pressure relative to the surrounding atmospheric pressure, while absolute pressure measures total pressure including atmospheric. A tire gauge reading of 32 psi means 32 psi above atmospheric pressure (about 14.7 psi at sea level), so the absolute pressure inside the tire is approximately 46.7 psia. In engineering, psig indicates gauge pressure and psia indicates absolute pressure. Most everyday instruments — tire gauges, blood pressure monitors, water pressure gauges — display gauge pressure. Scientific calculations, particularly gas law equations, require absolute pressure.

How does altitude affect atmospheric pressure?

Atmospheric pressure decreases with altitude because there is less air above you exerting weight. At sea level, standard pressure is 101,325 Pa (14.696 psi or 1 atm). At 1,500 meters (about 5,000 feet), pressure drops to roughly 84,600 Pa (12.27 psi). At the summit of Mount Everest (8,849 meters), pressure is only about 33,700 Pa (4.89 psi) — roughly one-third of sea level pressure. This reduction affects cooking (water boils at lower temperatures), breathing (less oxygen per breath), and engine performance (less air for combustion). Pressure altitude is a critical concept in aviation for determining aircraft performance.

Why is blood pressure measured in mmHg?

Blood pressure is measured in millimeters of mercury because the original sphygmomanometers (blood pressure cuffs) used a column of mercury to display the pressure reading. Italian physician Scipione Riva-Rocci invented the modern mercury sphygmomanometer in 1896, and the mmHg unit became the medical standard. Although most modern devices are digital and contain no mercury, the unit persists for historical consistency and because medical professionals worldwide are trained to interpret readings in mmHg. Normal blood pressure is approximately 120/80 mmHg, which equals about 16.0/10.7 kPa.

What pressure do scuba divers experience underwater?

Pressure increases by approximately 1 atmosphere for every 10.06 meters (33 feet) of seawater depth. At 10 meters, a diver experiences about 2 atm absolute (1 atm from the water plus 1 atm from the atmosphere above). At 30 meters, the pressure is about 4 atm absolute, or 58.8 psi. Recreational diving limits are typically 40 meters (5 atm or 73.5 psi). This increasing pressure affects gas volumes in the body and equipment according to Boyle's law, which is why divers must equalize ear pressure and ascend slowly to avoid decompression sickness.

What is the difference between bar and millibar?

One bar equals 1000 millibars (mbar). The millibar is identical to the hectopascal (hPa) — both equal 100 pascals. Millibars are the standard unit on weather maps and in aviation meteorology. Standard sea-level pressure is 1013.25 mbar or 1.01325 bar. The millibar provides a convenient scale for weather reporting because typical atmospheric pressure variations fall in the range of 950 to 1050 mbar, making changes easy to read without decimal points. Pilots receive altimeter settings in millibars (or hectopascals) outside the United States, where inches of mercury is used instead.

How do I convert between kPa and psi?

To convert kPa to psi, divide by 6.89476. To convert psi to kPa, multiply by 6.89476. For example, 220 kPa ÷ 6.89476 = 31.91 psi, and 35 psi × 6.89476 = 241.3 kPa. Many Asian and Australian tire pressure specifications use kPa. A quick mental shortcut is to divide kPa by 7 for an approximate psi value — for instance, 210 kPa ÷ 7 = 30 psi (exact: 30.46 psi). This approximation is accurate enough for most tire pressure checks.

What is Pascal's law and why is it important?

Pascal's law states that pressure applied to a confined fluid is transmitted undiminished in every direction throughout the fluid and acts with equal force on equal areas. This principle, formulated by Blaise Pascal in 1653, is the foundation of all hydraulic systems. In a hydraulic press, a small force applied to a small piston creates the same pressure on a larger piston, multiplying the force proportionally to the area ratio. Car brakes, hydraulic jacks, construction excavators, and aircraft control systems all rely on Pascal's law. The principle also explains why pressure at a given depth in a fluid is the same in all directions.

What are the highest and lowest pressures found in nature?

The highest natural pressures occur at the centers of stars and planets. The pressure at the center of the Earth is estimated at about 360 gigapascals (3.55 million atm). The core of the Sun reaches approximately 265 billion atm. At the other extreme, interstellar space has a pressure of roughly 10⁻¹⁴ pascal, and intergalactic voids are even lower. On Earth's surface, the lowest recorded atmospheric pressure was 870 hPa (25.69 inHg) in the eye of Typhoon Tip in 1979, while the highest was about 1083.8 hPa (32.01 inHg) recorded in Agata, Siberia, in 1968.

How accurate is this pressure converter?

This converter uses IEEE 754 double-precision floating-point arithmetic, providing approximately 15 to 17 significant decimal digits of precision. For all practical applications — tire pressure, weather monitoring, medical readings, and engineering calculations — the results are effectively exact. The calculations run entirely in your browser using JavaScript, with no rounding from server-side processing. The conversion factors are based on internationally agreed definitions, including the exact value of 1 atm = 101,325 Pa.

Can I use this converter offline?

Yes. Because all calculations run in your browser using client-side JavaScript, the pressure converter works without an internet connection once the page has loaded. No data is transmitted to any server during the conversion process. This makes it ideal for use in workshops, laboratories, medical facilities, and field work where internet access may be limited or unreliable. Simply bookmark this page for quick access anytime you need to convert between pascals, bar, atmospheres, psi, and millimeters of mercury.