How many pascals are in one atmosphere?

One standard atmosphere (1 atm) is exactly 101,325 pascals (Pa). This is an exact definition by the International System of Units (SI) and is not a rounded approximation. It is equivalent to 101.325 kilopascals (kPa), 0.101325 megapascals (MPa), or 1.01325 bar.

What is the difference between atm, Pa, and kPa?

The pascal (Pa) is the SI unit of pressure, defined as one newton per square metre. It is a very small unit, so kilopascals (kPa = 1,000 Pa) and megapascals (MPa = 1,000,000 Pa) are commonly used in engineering. The standard atmosphere (atm) is a historical unit defined as the mean atmospheric pressure at sea level: 101,325 Pa. In everyday settings, weather forecasters often use hectopascals (hPa), where 1 hPa = 100 Pa, so standard atmospheric pressure is 1,013.25 hPa.

When would I need to convert atm to pascals?

You typically need to convert atm to Pa when working with scientific calculations or equations where SI units are required, such as the ideal gas law (PV = nRT), where pressure must be in pascals if you are using SI values for other constants. Atmospheric pressure data may be given in atm in chemistry and physics textbooks, while engineering software and fluid dynamics calculations usually expect pascals or kilopascals. Weather data is commonly given in hectopascals (hPa) or millibars (mbar), which are equivalent.

ATM to Pascals Conversion Calculator

This calculator converts atmospheres (atm) to pascals (Pa) and back again, along with kilopascals, megapascals, bar, hectopascals, millibar and PSI, using the exact SI definition of 1 atm = 101,325 Pa. Enter a pressure in atmospheres, or pick a preset such as 1 atm, 2 atm or a near-vacuum value, and every unit updates instantly. If you already have a reading in pascals or kilopascals, use the second panel to convert it straight back to atmospheres without doing the maths yourself. The results bar shows pascals, kilopascals, megapascals and bar at a glance, with a second row giving hectopascals, millibar, PSI and the atmosphere value worked back from your pascal or kilopascal entry. A reference table lists common atm values from 0.001 up to 10 atm across pascals, kilopascals, bar and PSI, and a worked example walks through the default 1 atm conversion step by step so you can check the formula yourself. This suits chemistry and physics problems needing SI units, such as the ideal gas law, reading engineering specifications given in kPa or MPa, or translating meteorological pressure in hectopascals into atmospheres. Because the atm to Pa conversion is an exact SI definition rather than an estimate, the pascal, kilopascal, megapascal, bar, hectopascal and millibar figures are precise; only the PSI conversion involves a repeating decimal, so it is rounded to six significant figures.

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SI Definition 1 atm = 101,325 Pa exactly, per the International System of Units (SI). No rounding applied.

Enter Pressure in Atmospheres

Atmospheres (atm) e.g. 1, 2.5, 0.5

atm

Common preset values

Or Enter Pascals to Convert Back

Pascals (Pa) converts to atm

Kilopascals (kPa) converts to atm

kPa

Conversion Results

Pascals (Pa)
101,325
Pa = N/m²

Kilopascals (kPa)

101.325

kPa = 1,000 Pa

Megapascals (MPa)

0.101325

MPa = 1,000,000 Pa

Bar

1.01325

1 bar = 100,000 Pa

Hectopascals (hPa)

1,013.25

hPa = mbar (weather unit)

Millibar (mbar)

1,013.25

1 mbar = 1 hPa = 100 Pa

PSI

14.69595

Pounds per square inch

ATM (from Pa input)

1.0000

Atmospheres

Common ATM to Pa Conversions

Atmospheres (atm)	Pascals (Pa)	Kilopascals (kPa)	Bar	PSI

Worked Example: Default Inputs

Input: 1 atm

Formula: Pa = atm x 101,325

Pa = 1 x 101,325 = 101,325 Pa

kPa = 101,325 / 1,000 = 101.325 kPa

MPa = 101,325 / 1,000,000 = 0.101325 MPa

bar = 101,325 / 100,000 = 1.01325 bar

hPa = 101,325 / 100 = 1,013.25 hPa

PSI = 1 x 14.69595 = 14.69595 PSI

These match the calculator output above for 1 atm.

What is a Standard Atmosphere (atm)?

The standard atmosphere (symbol: atm) is a unit of pressure defined as exactly 101,325 pascals (Pa). It was originally intended to approximate the mean atmospheric pressure at sea level on Earth. It has been the internationally accepted definition since 1954. While it is no longer an SI unit, it remains widely used in chemistry, physics, and engineering, particularly when describing pressures close to ambient.

What is a Pascal (Pa)?

The pascal is the SI unit of pressure, named after the French mathematician and physicist Blaise Pascal. It is defined as one newton of force per square metre of area (1 Pa = 1 N/m²). Because atmospheric pressure is approximately 101,325 Pa, the pascal is quite small for everyday use. Kilopascals (kPa = 1,000 Pa) and megapascals (MPa = 1,000,000 Pa) are more practical in engineering contexts. Hectopascals (hPa = 100 Pa) are the standard unit in meteorology.

The Exact Conversion Formula

The conversion between atmospheres and pascals is exact, not an approximation:

Pa = atm x 101,325
kPa = atm x 101.325
MPa = atm x 0.101325
bar = atm x 1.01325
hPa = atm x 1,013.25
PSI = atm x 14.695948775... (approximately 14.69595 to 7 sig. figs.)

To convert pascals back to atmospheres: atm = Pa / 101,325.

Pressure Unit Reference Table

Unit	Symbol	Relation to Pa	1 atm equals
Pascal	Pa	1 Pa	101,325 Pa
Kilopascal	kPa	1,000 Pa	101.325 kPa
Megapascal	MPa	1,000,000 Pa	0.101325 MPa
Hectopascal	hPa	100 Pa	1,013.25 hPa
Millibar	mbar	100 Pa	1,013.25 mbar
Bar	bar	100,000 Pa	1.01325 bar
Pounds per square inch	psi	6,894.757... Pa	14.69595 psi
Millimetre of mercury	mmHg / Torr	133.322... Pa	760.000 mmHg

When to Use Pascals vs Atmospheres

Pascals are required when working with SI unit systems, such as the ideal gas law in SI form (PV = nRT, where R = 8.314 J/(mol K) and P must be in Pa). Atmospheres are convenient when describing conditions close to ambient pressure, such as stating that a reaction occurs at 3 atm rather than 303,975 Pa. In meteorology, hectopascals (hPa) are the international standard; standard sea-level pressure is 1,013.25 hPa. In engineering, kilopascals (kPa) and megapascals (MPa) are common for structural loads and hydraulic systems.

Related Calculators

Sources and method: The conversion factor 1 atm = 101,325 Pa is an exact definition from the International System of Units (SI), as established by the 10th General Conference on Weights and Measures (CGPM) in 1954 and confirmed in the SI Brochure (Bureau International des Poids et Mesures, 9th edition). The PSI conversion uses 1 lbf = 4.44822162 N and 1 in = 0.0254 m, giving 1 psi = 6,894.757... Pa.

This calculator is for reference and educational use. The conversion 1 atm = 101,325 Pa is exact by SI definition. Results for PSI and other non-SI units are accurate to at least 6 significant figures.