Pressure bar ↔ atm

1 atm = 1.01325 bar = 14.696 psi.

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  • Pick direction + enter value.
  • Read all units.

About this calculator

1 atmosphere is the defined standard sea-level pressure: exactly 101,325 Pa = 1.01325 bar = 14.696 psi = 760 mmHg. Bar is metric round number (100 kPa). For most casual use, atm and bar are interchangeable (within 1.3%). Underwater pressure increases ~1 bar per 10 meters depth — so at 30m, total pressure is ~4 atm (1 atm air + 3 from water).

Frequently asked

Why two near-identical units?+
atm = historical (sea-level standard). bar = metric (round 100 kPa). Both used; ~1.3% different.
Sea-level pressure varies?+
Yes — by altitude (drops ~12 mb per 100m), weather (storms drop 30-50 mb), latitude (~10 mb).
Underwater pressure?+
1 atm at surface + 1 atm per 10 m depth. Diver at 30m = 4 atm absolute.
Vacuum chamber?+
Below 1 atm = vacuum. "High vacuum" = below 10⁻³ Pa. "Ultra high vacuum" = below 10⁻⁷ Pa.
When use atm?+
Chemistry, biology, geology — historical convention. Engineering: Pa or bar. Medicine: mmHg.

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