What is standard sea-level atmospheric pressure in different units?

Standard atmospheric pressure at sea level is defined as 101,325 Pa. This equals 1013.25 hPa (or mbar), 29.9213 inHg, 760 mmHg (Torr), 101.325 kPa, 1.01325 bar, 1 atm, and 14.6959 psi. Weather forecasters most commonly use hPa (hectopascals), which are numerically identical to millibars (mbar). Aviation uses inHg in some regions and hPa in others.

What is typical barometric pressure in New Zealand?

New Zealand sea-level barometric pressure typically ranges from about 980 hPa during deep low-pressure systems (storms) to 1035 hPa during strong high-pressure systems (settled fine weather). The long-term average is close to the global standard of 1013.25 hPa. NZ MetService reports pressure in hPa. A reading above 1020 hPa generally indicates fine weather, while readings below 1000 hPa suggest unsettled or stormy conditions.

Why do weather apps show pressure in different units?

Different regions and fields use different pressure units. Most of the world, including New Zealand, Australia, and Europe, uses hPa (hectopascals), which are equal to millibars (mbar). The United States often uses inHg (inches of mercury), especially in aviation. Scientific contexts use Pa or kPa. Medical and laboratory contexts sometimes use mmHg (millimetres of mercury, also called Torr). Bar and atm appear in engineering and chemistry. All of these units can be converted exactly using fixed multiplication factors because they all measure the same physical quantity.

Barometric Pressure Conversion Calculator

This calculator converts barometric pressure between the eight units most commonly used in weather, aviation, science, and engineering: hPa (millibars), inHg, mmHg (Torr), kPa, Pa, bar, atm, and psi. Select the unit you are starting from, enter a pressure value, and every other unit updates immediately, so you never need to look up a conversion table or work through the multiplication by hand. The results table lists all eight units side by side and highlights your source unit, while quick preset buttons jump straight to standard sea-level pressure (1013.25 hPa), 1000 hPa, 29.92 inHg, or 760 mmHg. Below the calculator, a reference table shows typical hPa, inHg, mmHg, and kPa readings for situations such as fine and stormy weather in New Zealand, a record low from Cyclone Gita, the summit of Aoraki/Mt Cook, and aircraft cabin pressure, giving useful context for whatever figure you are working with. Use this tool when a weather forecast, barometer, altimeter, dive computer, or laboratory instrument gives you one unit and you need another, or to check how a MetService reading compares with an overseas source using different units. Every conversion uses fixed, exact multiplication factors defined by international standards (SI and ISO 80000-4), so the figures returned are precise rather than estimates, and the same numbers reappear in the worked example further down the page.

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Verified 2025 Conversion factors from SI definitions. Standard atmosphere: NIST/ISO 80000-4.

Enter a Pressure Value

Unit to convert from

Pressure value

hPa

Quick presets:

Conversion Results

Unit	Value
hPa (mbar)	1013.25
inHg	29.9213
mmHg (Torr)	760.00
kPa	101.325
Pa	101325
bar	1.01325
atm	1.00000
psi	14.6959

Reference Pressure Levels

Situation	hPa	inHg	mmHg	kPa
Standard atmosphere (sea level)	1013.25	29.92	760.00	101.33
Typical fine weather (NZ high)	1025	30.27	768.81	102.50
Typical stormy weather (NZ low)	985	29.09	738.81	98.50
Record NZ low (Cyclone Gita 2018)	950	28.05	712.56	95.00
Mt Cook summit (~3,754 m)	630	18.60	472.54	63.00
Aircraft cabin pressure (8,000 ft equiv.)	753	22.24	564.80	75.30

How Barometric Pressure Conversion Works

All barometric pressure units measure the same physical quantity: the force exerted by a column of air (or fluid) per unit area. They differ only in the size of the unit. Because the relationships between units are fixed constants, conversion is exact multiplication.

The calculator converts your input to pascals (Pa) first, then from pascals to every other unit using the following exact factors:

Unit	Pascals per unit	Formula (from Pa)
1 hPa (mbar)	100 Pa	Pa / 100
1 inHg (at 0 degC)	3386.389 Pa	Pa / 3386.389
1 mmHg (Torr)	133.322 Pa	Pa / 133.322
1 kPa	1000 Pa	Pa / 1000
1 Pa	1 Pa	Pa
1 bar	100,000 Pa	Pa / 100000
1 atm	101,325 Pa	Pa / 101325
1 psi	6894.757 Pa	Pa / 6894.757

Worked Example

Using the default value of 1013.25 hPa (standard sea-level pressure):

1013.25 hPa x 100 = 101,325 Pa
101,325 / 3386.389 = 29.9213 inHg
101,325 / 133.322 = 760.00 mmHg
101,325 / 1000 = 101.325 kPa
101,325 / 100,000 = 1.01325 bar
101,325 / 101,325 = 1.00000 atm
101,325 / 6894.757 = 14.6959 psi

These results match exactly what the calculator shows for the default input, confirming the conversions are correct.

Which Units Are Used Where?

hPa and mbar are numerically identical (1 hPa = 1 mbar exactly) and are the standard for meteorology worldwide, including New Zealand's MetService, Australian Bureau of Meteorology, and the World Meteorological Organization (WMO).

inHg (inches of mercury) is used in aviation in the United States and some other countries for altimeter settings. New Zealand aviation uses hPa.

mmHg and Torr are used in medicine (blood pressure, vacuum systems) and chemistry. One Torr equals exactly 1 mmHg by definition since 2019 (they were previously slightly different).

Pa and kPa are the SI units. Scientific papers and engineering standards typically use Pa or kPa. Tyre pressures in New Zealand are often given in kPa.

bar is widely used in engineering, industrial gas, and scuba diving. 1 bar is close to but not exactly 1 atm (1 bar = 0.98692 atm).

psi is common in the United States and some industrial applications. Tyre pressures in older manuals may be given in psi.

Barometric Pressure and the Weather

Atmospheric pressure at any location is the weight of the air column above that point. It naturally decreases with altitude (roughly 1 hPa for every 8 m gain near sea level). Meteorologists correct station pressure to sea-level pressure (QNH) so that readings from different altitudes can be compared.

In New Zealand, pressure typically ranges from around 950 hPa in a severe tropical cyclone to about 1040 hPa during a strong winter anticyclone. A rapid pressure drop (more than 5 hPa in 3 hours) is a sign of rapidly deteriorating weather. A steady rise indicates improving conditions.

Related Calculators

Science and Engineering Calculators: full hub for science and engineering tools.
Air Pressure at Altitude Calculator: estimate pressure at any altitude using the barometric formula.
kPa to psi Conversion: quick converter for tyre pressures and industrial use.
Bar to psi Conversion: convert between bar and psi for diving, gas, and engineering.
atm Conversion: convert standard atmospheres to and from other pressure units.

Sources and method: Conversion factors from NIST (National Institute of Standards and Technology) and ISO 80000-4. Standard atmosphere definition: 101,325 Pa exactly (Resolution 4 of the 10th CGPM, 1954). inHg factor based on mercury density at 0 degC and standard gravity (9.80665 m/s2). mmHg/Torr redefinition: BIPM 2019.

This calculator converts barometric pressure between common units using exact SI-defined conversion factors. The inHg factor uses mercury density at 0 degrees Celsius; some aviation and weather references use a slightly different factor based on 15 degrees Celsius (3376.85 Pa/inHg). For precision work, check the specific definition used by your instrument or standard.