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What is ATM to Pascals Pressure Converter?

atm to pascals, atmospheric pressure This tool runs entirely in your browser. No data is sent to any server, and no signup is needed.

Atmospheres to Pascals Converter

Atmospheric pressure: 1 atm = 101,325 Pa exactly. Convert atm to Pa, bar, psi, mmHg, torr.

Input value

Result

101325

About this converter

The standard atmosphere (atm) is a fixed reference pressure defined as exactly 101,325 pascals (Pa), originally chosen to approximate mean air pressure at sea level. The pascal is the SI coherent unit of pressure (1 Pa = 1 N/m²). Converting between the two is a single exact multiplication.

How it works

The General Conference on Weights and Measures (CGPM, 1954, Resolution 4) fixed the standard atmosphere at exactly 101,325 Pa. NIST SP 811 (Appendix B.8) retains that value, and BIPM lists atm as a non-SI unit accepted for limited use. The conversion is therefore an integer ratio, not an approximation.

1 atm = 101,325 Pa                (exact, CGPM 1954)
1 atm = 1.01325 bar               (since 1 bar = 100,000 Pa)
1 atm = 14.6959487755 psi
1 atm = 760 mmHg = 760 torr       (by definition of torr)

To convert: multiply atm by 101,325 to get Pa; divide Pa by 101,325 to get atm.

Worked example

A chemistry student needs to express the partial pressure of oxygen in dry air at standard pressure. Atmospheric oxygen is 20.95 percent by mole. Standard pressure is 1 atm.

Total pressure in Pa: 1 atm x 101,325 Pa/atm = 101,325 Pa.
Partial pressure of O₂: 101,325 Pa x 0.2095 = 21,227.6 Pa.
Convert back to atm: 21,227.6 / 101,325 = 0.2095 atm (sanity check).
In kPa for plotting: 21.23 kPa, the value typically quoted in respiratory physiology.

Result: At 1 atm (101,325 Pa), atmospheric oxygen partial pressure is 21,228 Pa (21.23 kPa, 0.2095 atm, 159.2 mmHg). The mmHg value is the one a clinician uses to interpret arterial blood gas results.

Reference table

atm	Pa	kPa	Context
0.01	1,013.25	1.013	Mars surface pressure (avg)
0.5	50,662.5	50.66	Pressure at 5,500 m altitude
1	101,325	101.325	Sea level standard
2	202,650	202.65	10 m underwater (gauge + 1 atm)
10	1,013,250	1,013.25	~90 m underwater
100	10,132,500	10,132.5	Industrial hydrostatic test
200	20,265,000	20,265	Scuba tank fill pressure
9,000	9.1e+08	9.1e+05	Venus surface pressure

Common pitfalls

Atm versus bar. 1 atm = 1.01325 bar; they are NOT the same. Older textbooks and pre-1982 chemistry data use 1 atm as the standard reference. IUPAC switched to 1 bar (= 100,000 Pa) as standard pressure in 1982. Enthalpy and entropy tables published since then use bar; older values use atm. Equilibrium constants differ by a small but real factor.
Gauge vs absolute. Atm is always absolute. If a tire reads 30 psi gauge, the absolute pressure is roughly 30 + 14.7 = 44.7 psi = 3.04 atm. Gas-law calculations (PV = nRT) require absolute pressure - never plug gauge readings in directly.
Altitude is non-linear. Pressure does not drop 1 atm per 10 km; it drops exponentially per the barometric formula. At 5,500 m altitude pressure is ~0.5 atm, at 16 km it is ~0.1 atm, at 80 km it is ~10^-5 atm.
Confusing atm with technical atmosphere (at). 1 atm (standard atmosphere) = 101,325 Pa. 1 at (technical atmosphere) = 98,066.5 Pa = 1 kgf/cm². They differ by 3.3 percent. Many older European hydraulic specs use at.
Torr is not mmHg under all conditions. 1 torr is defined as exactly 1/760 atm = 133.3224 Pa. 1 conventional mmHg is 133.3224 Pa as well, BUT a real mercury column varies slightly with temperature and local gravity. For lab and medical work they are interchangeable; for primary metrology they are not.

Related tools and references

bar to psi Tire pressure converter Kelvin to Celsius Glossary

Frequently asked questions

What is 1 atm in pascals exactly?

One standard atmosphere is exactly 101,325 Pa by definition (CIPM 1954, retained in BIPM SI Brochure). It is not measured; it is a fixed reference value originally meant to approximate mean sea-level air pressure at 0 degC and 45 degrees latitude.

How does atm compare to bar, psi, mmHg, and torr?

1 atm = 101,325 Pa = 1.01325 bar = 14.6959 psi = 760 mmHg = 760 torr (1 torr is defined as exactly 1/760 atm). The bar is about 1.3 percent smaller than 1 atm; psi is the US customary unit; mmHg dominates clinical medicine.

Is atm gauge or absolute pressure?

Atm is always absolute by convention - it is a fixed reference value, not a measurement relative to ambient. When you see "standard pressure" in chemistry (gas law calculations, STP) it means 1 atm absolute. Gauge pressure is reported in bar-g or psig, never atm.

Why does science use pascals rather than atm?

The pascal (Pa = N/m^2) is the coherent SI unit and slots directly into mechanical, fluid, and thermodynamic equations without conversion factors. IUPAC defines standard pressure for thermodynamics as 100,000 Pa (1 bar), not 1 atm, since 1982. Pa, kPa, MPa scale cleanly; atm does not.

Sources

CGPM (1954) Resolution 4, definition of standard atmosphere as 101,325 Pa.
BIPM (2019) The International System of Units (SI), 9th edition, Table 8.
NIST Special Publication 811 (2008) Guide for the Use of the International System of Units, App. B.8.
IUPAC (1982) standard pressure recommendation: 1 bar replaces 1 atm.

Last updated 2026-05-28.