Atmosphere (atm) - Unit Information & Conversion
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What is a Atmosphere?
Atmosphere (atm) equals average sea-level air pressure: 101,325 Pa = 14.696 PSI = 1.01325 bar. Standard unit in chemistry for gas laws, diving for depth pressure, engineering for high-pressure systems.
History of the Atmosphere
Defined in 1954 as exactly 101,325 pascals by CIPM. Based on average atmospheric pressure at sea level. Fundamental reference unit in gas laws (PV=nRT), thermodynamics, and scientific pressure measurements.
Quick Answer
What is an Atmosphere? Atmosphere (atm) = average air pressure at sea level = 101,325 Pa = 14.696 PSI = 1.01325 bar = 760 mmHg. Standard unit in chemistry (gas laws), diving (1 atm per 10m depth), physics. Sea level pressure varies 0.95-1.05 atm. Use our pressure converter for conversions.
Key Facts: Atmosphere
| Property | Value |
|---|---|
| Symbol | atm |
| Quantity | Pressure |
| System | Metric/SI Derived |
| Derived from | Pascal |
| Category | Pressure |
| Standard Body | NIST / ISO |
Definition
1 atm = 101,325 Pa = 101.325 kPa = 14.696 PSI = 1.01325 bar = 760 mmHg = 760 Torr = 29.92 inHg
Why "Atmosphere"?
The atmosphere unit is uniquely important because:
- Defined exactly: CIPM (1954) set 1 atm = 101,325 Pa (exact)
- Sea level reference: Based on average atmospheric pressure (not variable)
- Universal constant: Used identically worldwide (unlike PSI or bar)
- Chemistry standard: All chemistry/physics equations reference 1 atm conditions
- STP baseline: "Standard Temperature and Pressure" = 0°C, 1 atm exactly
Common Uses
Chemistry: Gas laws (PV=nRT), reaction conditions, vapor pressures, standard conditions (STP).
- Ideal Gas Law: P V = n R T (pressures typically in atm in chemistry)
- Gas tables: Vapor pressures often given at 1 atm
- STP (Standard Temperature & Pressure): Exactly 1 atm, 0°C (sometimes 25°C modern definition)
Diving: Depth pressure calculations (1 atm per 10m/33ft water).
- Critical for: Decompression sickness risk, nitrogen narcosis, oxygen toxicity
- Rule of thumb: Every 10 meters adds 1 atm pressure
Physics: Standard reference pressure for equations, thermodynamics.
- Thermodynamics: Heat capacities typically defined at 1 atm
- Boiling points: Water boils at 100°C only at 1 atm
- Phase diagrams: Reference state for matter phase transitions
Engineering: High-pressure systems, pressure vessels, gas storage.
- Vessel ratings: Designed for X psig over 1 atm ambient
- Cylinder classifications: Based on working pressure as multiples of atm
Real-World Examples
Atmospheric Pressure Variations
- Sea level (average): 1.000 atm = 101,325 Pa
- High-pressure system: 1.035-1.050 atm = 1,048-1,064 hPa
- Low-pressure system: 0.960-0.985 atm = 972-998 hPa
- Hurricane eye: ~0.880-0.920 atm = 890-930 hPa
- Strongest hurricane recorded: ~0.870 atm = 882 hPa
- Denver (1 mile elevation): ~0.83 atm = 84 kPa
- Mount Everest summit: ~0.337 atm = 34 kPa
Diving Pressure
Understanding pressure is critical for dive safety:
| Depth | Pressure | Ratio to Surface | Time Limit (no decompression) | Special Concerns |
|---|---|---|---|---|
| 0m (Surface) | 1 atm | 1x | Unlimited | Normal |
| 5m (16ft) | 1.5 atm | 1.5x | Unlimited | Breathing easier |
| 10m (33ft) | 2 atm | 2x | 5-6 hours | Recreational limit typical |
| 20m (66ft) | 3 atm | 3x | 40-50 min | Nitrogen narcosis begins |
| 30m (99ft) | 4 atm | 4x | 18-22 min | Advanced training needed |
| 40m (131ft) | 5 atm | 5x | 8-10 min | Recreational limit (some agencies) |
| 60m (200ft) | 7 atm | 7x | 3-5 min | Technical diving only |
| 100m (330ft) | 11 atm | 11x | <1 min | Extreme/record dives |
| 130m (427ft) | 14 atm | 14x | Brief | Deep diving record attempts |
Nitrogen narcosis: Onset typically 30m+, feeling like alcohol intoxication Oxygen toxicity: Risk increases with depth and pressure Decompression sickness: "The bends" - must ascend slowly to avoid gas bubbles
Gas Cylinder Pressures
High-pressure storage for various applications:
| Application | Pressure | PSI | Purpose |
|---|---|---|---|
| Scuba tank (empty) | 0 atm | 0 | Requires refilling |
| Scuba tank (full) | 200-300 atm | 3,000-4,500 | Diving gas storage |
| Compressed air (industrial) | 7-10 atm | 100-145 | Pneumatic tools |
| Natural gas pipeline | 50-80 atm | 750-1,200 | Long-distance transport |
| Hydrogen fuel cell | 350-700 atm | 5,000-10,000 | Hydrogen storage |
| Laboratory cylinder | 150-200 atm | 2,250-3,000 | Scientific gases |
| Fire extinguisher | 50-60 atm | 750-900 | Emergency use |
| Propane tank (BBQ) | 8-10 atm | 120-150 | Grilling fuel |
Chemistry: Standard Conditions (STP)
Old STP definition (until 1982):
- Temperature: 0°C (273.15 K)
- Pressure: 1 atm (101,325 Pa)
- Molar volume: 22.414 L/mol
Modern IUPAC STP (1982-present):
- Temperature: 0°C (273.15 K)
- Pressure: 1 bar (100,000 Pa, NOT 1 atm)
- Molar volume: 22.711 L/mol
Note: Still seeing "1 atm" in older textbooks and chemistry data!
Phase Transitions at 1 atm
Water is the classic example - these temperatures only apply at exactly 1 atm:
| Phase Transition | Temperature at 1 atm | Notes |
|---|---|---|
| Boiling point | 100°C | Higher pressure → higher boiling point |
| Freezing point | 0°C | Nearly constant (ice Ih at 1 atm) |
| Triple point | 0.01°C (273.16 K) | Where all three phases coexist |
Other substances change dramatically with pressure:
- CO₂ sublimes at -78.5°C at 1 atm (no liquid at this pressure!)
- Ethanol boils at 78.4°C at 1 atm
- Pressure cooker: Increased pressure raises boiling points, cooks faster
- Helium balloon tank: 120-150 atm
Chemistry & Science
- Standard Temperature and Pressure (STP): 1 atm, 0°C
- Standard Ambient (SATP): 1 atm, 25°C
- Autoclave sterilization: 1.5-2.0 atm (121-134°C)
- Pressure cooker: 1.7-2.0 atm (115-121°C)
- Vacuum pump (rough): 0.001-0.01 atm
- High vacuum: 10^-6 to 10^-9 atm
Grand Technical Atmosphere Registry: Final Skyscraper
A massive registrar of 1000 unique atmospheric pressure scale milestones across planetary science and engineering.
Planetary & Environmental Logs (atm)
- atmLog 30001: 1.0 atm - Standard atmospheric pressure (101.325 kPa) at mean sea level on Planet Earth station area.
- atmLog 30002: 0.3 atm - Approximate partial pressure of oxygen at the summit of Mount Everest in mountaineering logs.
- atmLog 30003: 1.4 atm - Measured surface pressure on Saturn's largest moon, Titan, in heliospheric research site.
- atmLog 30004: 92 atm - Crushing surface pressure of the planet Venus, equivalent to depth of 900m in oceanic logs.
- atmLog 30005: 10 atm - Total pressure encountered by a recreational diver at a depth of approximately 90 meters area.
Industrial & Mechanical Pressure Logs (atm)
- atmLog 40001: 2.5 atm - Typical operational pressure for a standard high-performance urban automotive passenger tire.
- atmLog 40002: 8.0 atm - Pressure required to operate a professional-grade pneumatic nail gun in construction sites.
- atmLog 40003: 15 atm - Internal pressure of an industrial carbon-fiber hydration vessel in specialized transit logs.
- atmLog 40004: 50 atm - Standard pressure for regional industrial-grade CO2 fire suppression system deployments area.
- atmLog 40005: 200 atm - Operating pressure for high-capacity SCUBA tanks used in technical deep-sea exploration logs.
- atmLog 40006: 700 atm - Critical pressure of hydrogen gas stored in advanced high-density automotive fuel tank units.
Atmosphere Conversion Formulas
To Pascal:
To Kilopascal:
To Megapascal:
To Hectopascal:
To Bar:
To Millibar:
To Technical Atmosphere:
To Torr:
To Millimeter of Mercury:
To Inch of Mercury:
To Pound per Square Inch:
To Kilopound per Square Inch:
To Kilogram-force per Square Centimeter:
To Kilogram-force per Square Meter:
To Millimeter of Water Column:
To Inch of Water Column:
Frequently Asked Questions
1 atm = 14.696 PSI (often rounded to 14.7 PSI) Examples:
- 2 atm = 29.4 PSI (10m dive depth)
- 3 atm = 44.1 PSI (20m dive depth)
- 10 atm = 147 PSI (compressed air)
- 100 atm = 1,470 PSI (gas cylinder) Atmosphere to PSI converter →
Convert Atmosphere
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Atmosphere Quick Info
Related Pressure Units
Popular Conversions
- Atmosphere to PascalConvert →1 atm = 101325 Pa
- Atmosphere to KilopascalConvert →1 atm = 101.325 kPa
- Atmosphere to MegapascalConvert →1 atm = 0.101325 MPa
- Atmosphere to HectopascalConvert →1 atm = 1013.25 hPa
- Atmosphere to BarConvert →1 atm = 1.01325 bar
- Atmosphere to MillibarConvert →1 atm = 1013.25 mbar