Barometric Pressure Conversion Calculator
Enter a pressure reading in any unit and this calculator converts it to all nine other barometric pressure units at once. Choose your source unit, type the value, and the hPa, mbar, inHg, mmHg, atm, kPa, Pa, psi, bar, and MPa equivalents appear instantly. A gauge shows where your reading sits relative to standard atmospheric pressure. The steps panel shows the exact arithmetic, an altitude chart shows how pressure varies from sea level to 10 000 m, and a reference table lists key pressure benchmarks.
Formula
Worked example
Convert 29.92 inHg to all units: 29.92 x 33.8639 = 1013.25 hPa = 1013.25 mbar = 760.00 mmHg = 101.325 kPa = 101325 Pa = 14.696 psi = 1.01325 bar = 0.101325 MPa = 1.00000 atm. This is the standard atmosphere value at sea level.
What is barometric pressure?
Barometric pressure, also called atmospheric pressure, is the force exerted by the weight of the atmosphere above a given point. At sea level, the standard value is 1013.25 hPa (hectopascals), which equals 29.9213 inHg, 760.00 mmHg, 14.6959 psi, or exactly 1 standard atmosphere. Pressure decreases with altitude because there is less air above. It also changes with weather: low-pressure systems draw in moist, rising air and are associated with clouds and rain, while high-pressure systems press dry, descending air down and bring clear skies. Meteorologists track pressure tendency (how fast it rises or falls) as much as the absolute value. A fall of 6 hPa or more in three hours is classified as a rapid fall, and 20 hPa in 24 hours is sometimes called explosive cyclogenesis.
Which units are used and where?
Pressure unit choice depends heavily on field and geography. hPa and its identical twin mbar (1 hPa = 1 mbar exactly) are the standard units for surface weather analysis worldwide and for aviation QNH settings outside the United States. inHg is the standard for US aviation altimeter settings and domestic US weather broadcasts. mmHg (also called Torr) is widely used in medicine for blood pressure and in vacuum systems. kPa is the official SI-preferred reporting unit in Canada and Australia. Pa is the SI base unit, used in scientific calculations and building engineering. psi is common in US industrial settings, tire pressure, and equipment ratings. bar and mbar appear in European engineering, scuba diving gear, and older meteorological charts. MPa (megapascal) is used in materials testing, hydraulics, and high-pressure engineering.
How to convert between pressure units - the hub method
The most reliable approach treats hPa (= mbar) as the conversion hub. To convert any unit to hPa: multiply inHg by 33.8639; multiply mmHg by 1.33322; multiply atm by 1013.25; multiply kPa by 10; multiply Pa by 0.01; multiply psi by 68.9476; multiply bar by 1000; multiply MPa by 10 000. To convert hPa to any other unit, multiply by the inverse of those factors (for example, hPa to inHg: multiply by 0.029530; hPa to psi: multiply by 0.014504). For a two-step conversion such as inHg to psi: first convert inHg to hPa (x 33.8639), then hPa to psi (x 0.014504). The steps panel above shows every step with your actual numbers.
Pressure and altitude: the barometric formula
Pressure drops approximately 12 hPa for every 100 metres of altitude gain near sea level (roughly 1 hPa per 8 m). The precise relationship is given by the ISA barometric formula for the troposphere: P = 1013.25 x (1 - 0.0000226577 x altitude_m)^5.25588. At 1000 m, standard pressure is about 899 hPa; at 3000 m (roughly Denver to base camp), about 701 hPa; at the summit of Mount Everest (8849 m), about 337 hPa - one third of sea level. This relationship is why pilots must correct their altimeters: they set QNH (current sea-level pressure) so the instrument reads altitude above mean sea level, or switch to standard 1013 hPa / 29.92 inHg above the transition altitude for consistent separation between aircraft.
Pressure in medicine and science: mmHg, Pa, and MPa
In clinical medicine, blood pressure and gas exchange are reported in mmHg. Normal arterial blood pressure is 120/80 mmHg systolic/diastolic; atmospheric pressure at sea level is 760 mmHg. Partial pressures of blood gases (oxygen, carbon dioxide) also use mmHg or kPa depending on country. In physics and materials science, the pascal is fundamental: material tensile strength is given in MPa; deep-sea pressures at the bottom of the Mariana Trench reach about 110 MPa (1100 bar). Vacuum chambers for semiconductor manufacturing are measured in Pa or millitorr. Understanding which unit is expected in each context prevents potentially dangerous misreadings in clinical and engineering settings.
Barometric pressure benchmarks and conversions
| Condition / landmark | hPa / mbar | inHg | mmHg | kPa | psi | atm | bar |
|---|---|---|---|---|---|---|---|
| Absolute record low (Typhoon Tip, 1979) | 870 | 25.69 | 652.6 | 87.0 | 12.62 | 0.8584 | 0.870 |
| Category 5 hurricane (central pressure) | 900 | 26.58 | 675.1 | 90.0 | 13.05 | 0.8882 | 0.900 |
| Deep depression / storm | 960 | 28.35 | 720.1 | 96.0 | 13.92 | 0.9474 | 0.960 |
| Low pressure system | 990 | 29.23 | 742.6 | 99.0 | 14.36 | 0.9771 | 0.990 |
| Denver, CO (elev. ~1609 m) | 997 | 29.44 | 747.8 | 99.7 | 14.46 | 0.9838 | 0.997 |
| Standard atmosphere (sea level) | 1013.25 | 29.92 | 760.0 | 101.3 | 14.70 | 1.0000 | 1.013 |
| Aircraft cabin (cruise altitude) | 1013 | 29.92 | 760.0 | 101.3 | 14.70 | 1.000 | 1.013 |
| Typical fair weather (high) | 1020 | 30.12 | 765.1 | 102.0 | 14.79 | 1.0067 | 1.020 |
| Strong high pressure | 1030 | 30.42 | 772.6 | 103.0 | 14.94 | 1.0165 | 1.030 |
| Absolute record high (Tosontsengel, 2001) | 1084.8 | 32.03 | 813.6 | 108.5 | 15.73 | 1.0707 | 1.085 |
Key reference points with exact or rounded equivalents across all nine pressure units. Standard atmosphere = 1013.25 hPa exactly. inHg and mmHg values are for mercury at 0 degrees C.
Frequently asked questions
What is standard barometric pressure at sea level?
Standard atmospheric pressure at sea level is exactly 1013.25 hPa (= 1013.25 mbar), which equals 29.9213 inHg, 760.00 mmHg (Torr), 101.325 kPa, 101325 Pa, 14.6959 psi, 1.01325 bar, 0.101325 MPa, and exactly 1 atm. This is the International Standard Atmosphere (ISA) baseline used in aviation, meteorology, and physics.
Is hPa the same as mbar?
Yes, 1 hectopascal (hPa) is exactly equal to 1 millibar (mbar). Both equal 100 pascals. The meteorological community switched from mbar to hPa in the 1980s to align with SI units, but the numbers on weather maps did not change because the unit size is identical.
How do I convert inHg to hPa?
Multiply inches of mercury by 33.8639. For example, the standard US weather-report value of 29.92 inHg equals 29.92 x 33.8639 = 1013.44 hPa. To go the other direction, multiply hPa by 0.029530. A convenient shortcut: 30.00 inHg is approximately 1016 hPa.
What is a low barometric pressure reading and what does it mean?
Any reading significantly below 1013.25 hPa is considered low. Values below 1000 hPa often indicate active weather systems. Below 980 hPa signals a strong low, below 960 hPa a severe depression or hurricane. The all-time record low for a non-tornado surface reading is 870 hPa inside Typhoon Tip in 1979. Falling pressure typically precedes deteriorating weather; rising pressure signals improvement.
How does altitude affect barometric pressure?
Pressure decreases by roughly 12 hPa (about 0.35 inHg) for every 100 metres of altitude at sea level, and more slowly at higher altitudes. At the summit of Mount Everest (8849 m) the average pressure is about 337 hPa - one third of sea level. The altitude chart on this page shows the full ISA pressure profile from 0 to 10 000 m, and the insight panel estimates the altitude corresponding to your entered pressure.
What is the difference between mmHg and Torr?
For practical purposes, mmHg and Torr are the same: 1 Torr was defined to exactly equal 1 mmHg for many years. The modern SI definition makes them differ by about 0.000014 %, which is negligible for weather and medical use. Both are defined relative to mercury at 0 degrees Celsius and standard gravity (9.80665 m/s2).
Why is aviation altimeter setting given in inHg in the US but hPa elsewhere?
The US Federal Aviation Administration standardised on inches of mercury decades ago and has retained it for domestic operations. ICAO (International Civil Aviation Organization) recommends hPa for international use, and most of the world follows ICAO. When flying internationally, US pilots must convert: 29.92 inHg is equivalent to 1013 hPa, and most modern avionics can display both units.
What is MPa and when is it used for pressure?
MPa stands for megapascal - 1 MPa equals 1 000 000 Pa, or 10 bar, or about 145 psi. Standard atmospheric pressure is only 0.101325 MPa, so MPa is not used for weather. It appears in materials testing (steel yield strength is typically 250 to 500 MPa), hydraulic systems (car brakes operate at 10 to 20 MPa), and deep-sea pressure calculations. The calculator outputs the MPa value so engineers can verify atmospheric loads on structures.