ATM to PSI Conversion: Atmospheric Pressure Explained
1 ATM (standard atmosphere) equals 14.696 PSI.To convert ATM to PSI, multiply by 14.6959. For example, 5 ATM × 14.6959 = 73.48 PSI. To convert PSI to ATM, divide by 14.6959.
What Is a Standard Atmosphere (ATM)?
A unit of pressure defined as exactly 101,325 pascals (Pa), equal to 14.6959 PSI or 1.01325 bar. The standard atmosphere was defined to represent mean atmospheric pressure at sea level and is used as a reference baseline in thermodynamics, chemistry, and pressure system specifications. It is not part of the SI system but is widely recognized and used internationally.
The standard atmosphere (atm) serves as a reference point — a defined baseline against which other pressures can be compared. It is not the pressure at any specific location at any specific time, but a standardized value used for calculation and specification purposes. Actual atmospheric pressure at any location varies continuously with weather, altitude, and temperature.
ATM to PSI Formula
Converting between ATM and PSI is a direct multiplication or division using the defined conversion factor. ATM converts to PSIA (absolute pressure), not PSIG (gauge pressure). For a complete explanation of the difference between absolute and gauge pressure, see our guide on BARG to PSI and gauge pressure.
Exact value: 1 atm = 14.695948775 PSI | Standard precision: 14.696 PSI | Field estimate: 14.7 PSI
Example: 3 ATM × 14.6959 = 44.09 PSI | 100 PSI ÷ 14.6959 = 6.805 ATM
Converting ATM to PSIG (Gauge Pressure)
ATM and PSIA are both absolute pressure units, referenced to a perfect vacuum. To convert ATM to gauge pressure (PSIG — the reading your gauge shows), subtract one atmosphere after converting:
Example: 2 ATM × 14.6959 = 29.39 PSIA | 29.39 − 14.696 = 14.69 PSIG
At 1 ATM (sea level): (1 × 14.6959) − 14.696 = 0 PSIG — your gauge reads zero at atmospheric, as expected.
ATM to PSI Reference Chart
The following chart provides ATM to PSI conversions across a range spanning from partial vacuum through industrial hydraulic pressures, with practical context for each value.
| ATM | PSIA | PSIG (approx.) | Practical Context |
|---|---|---|---|
| 0.25 atm | 3.67 PSIA | — (vacuum) | High altitude (~30,000 ft / jet cruising altitude) |
| 0.5 atm | 7.35 PSIA | — (vacuum) | ~18,000 ft elevation, partial vacuum |
| 0.75 atm | 11.02 PSIA | — (vacuum) | ~8,000 ft elevation (mountainous terrain) |
| 1.0 atm | 14.696 PSIA | 0 PSIG | Standard sea-level atmosphere — gauge reads zero |
| 1.5 atm | 22.04 PSIA | 7.35 PSIG | Approximately 17 ft underwater |
| 2.0 atm | 29.39 PSIA | 14.69 PSIG | Approximately 33 ft underwater (scuba reference) |
| 3.0 atm | 44.09 PSIA | 29.39 PSIG | Approximately 66 ft underwater |
| 5.0 atm | 73.48 PSIA | 58.78 PSIG | Light pneumatic / compressed air range |
| 10 atm | 146.96 PSIA | 132.26 PSIG | Standard shop air pressure |
| 20 atm | 293.9 PSIA | 279.2 PSIG | Low hydraulic system pressure |
| 50 atm | 734.8 PSIA | 720.1 PSIG | Medium hydraulic circuits |
| 100 atm | 1,470 PSIA | 1,455 PSIG | Moderate high-pressure hydraulics |
| 200 atm | 2,939 PSIA | 2,924 PSIG | High-pressure hydraulics (~3,000 PSI system) |
| 350 atm | 5,143 PSIA | 5,129 PSIG | Ultra-high-pressure hydraulic systems |
PSIA = absolute pressure. PSIG = gauge pressure (PSIA − 14.696). Conversion factor: 1 atm = 14.6959 PSI. Source: NIST — Standard Atmosphere Definition.
ATM vs. Other Pressure Units
The atmosphere is one of several pressure units in common use across industrial, scientific, and engineering contexts. The following table shows how 1 ATM relates to each major pressure unit — useful when translating between international specifications and U.S.-standard documentation.
| Pressure Unit | 1 ATM Equals | To Convert FROM ATM | Common Use |
|---|---|---|---|
| PSI (absolute) | 14.696 PSI | ATM × 14.6959 | U.S. industrial, hydraulics |
| bar | 1.01325 bar | ATM × 1.01325 | European industrial, ISO specs |
| kPa | 101.325 kPa | ATM × 101.325 | SI standard, scientific |
| MPa | 0.101325 MPa | ATM × 0.101325 | High-pressure engineering |
| in WC | 406.8 in WC | ATM × 406.8 | HVAC, low-pressure gas |
| mmHg | 760 mmHg | ATM × 760 | Medical, barometric pressure |
| inHg | 29.92 inHg | ATM × 29.92 | Aviation, weather stations |
| Pa (pascal) | 101,325 Pa | ATM × 101,325 | SI base unit, scientific |
For full conversion guides, see ARG Industrial pressure conversion series: PSI to Bar | BARG to PSI | PSI to Inches of Water Column.
ATM, PSIA, and PSIG — Absolute vs. Gauge Pressure
One of the most important distinctions in pressure measurement is the difference between absolute and gauge pressure. ATM is an absolute pressure unit — it includes atmospheric pressure in its value. This makes it directly equivalent to PSIA, not PSIG.
The Relationship at Sea Level
- 1 ATM = 14.696 PSIA— both absolute, both include atmospheric baseline
- 1 ATM = 0 PSIG— at atmospheric pressure, a gauge reads zero
- 2 ATM = 29.39 PSIA = 14.69 PSIG— one atmosphere above ambient
How Altitude Affects Atmospheric Pressure
Standard atmospheric pressure (1 ATM = 14.696 PSI) is defined at sea level. In practice, atmospheric pressure decreases with altitude as the weight of the overlying air column decreases. This has practical implications for compressed air systems, pump NPSH calculations, and pressure vessel design at elevation.
| Elevation | Atmospheric Pressure (PSIA) | Atmospheric Pressure (ATM) | Notes |
|---|---|---|---|
| Sea level (0 ft) | 14.696 PSIA | 1.000 atm | Standard reference |
| 1,000 ft | 14.17 PSIA | 0.964 atm | Low-elevation cities |
| 2,000 ft | 13.66 PSIA | 0.930 atm | — |
| 3,000 ft | 13.17 PSIA | 0.897 atm | — |
| 5,000 ft | 12.23 PSIA | 0.832 atm | Denver, CO elevation range |
| 7,000 ft | 11.34 PSIA | 0.772 atm | High-elevation inland areas |
| 10,000 ft | 10.10 PSIA | 0.688 atm | High mountain passes |
| 20,000 ft | 6.75 PSIA | 0.460 atm | High-altitude aviation |
Atmospheric pressure at altitude. Source: NOAA — Atmospheric Pressure Reference. Values are approximate standard atmosphere model values.
ATM in Industrial & Hydraulic System Context
In day-to-day industrial and hydraulic work, ATM is rarely the primary specification unit. PSI and bar dominate U.S. and international specifications respectively. ATM appears most frequently in:
- Scientific and process documentationwhere thermodynamic calculations require absolute pressure references
- Pressure vessel standardswhere absolute pressure is used for design calculations
- Gas and fluid properties tablesthat reference standard conditions (typically defined at 1 ATM)
- Equipment manuals from scientific instrument manufacturersthat express specifications in ATM or bar-absolute
- Vacuum system specificationswhere pressure is expressed as a fraction of an atmosphere
For hydraulic hose, fittings, and industrial fluid power components, specifications are always in gauge pressure — PSI or bar. Understanding ATM helps technicians correctly interpret absolute-pressure documentation and convert it to gauge units for component selection.
Frequently Asked Questions
1 standard atmosphere equals 14.696 PSI(exact: 14.695948775 PSI). This is sea-level atmospheric pressure under standard conditions as defined by NIST. For quick estimates, 14.7 PSI is commonly used.
Multiply the ATM value by 14.6959to get PSIA (absolute). Example: 5 ATM × 14.6959 = 73.48 PSIA. To get PSIG (gauge), subtract 14.696: 73.48 − 14.696 = 58.78 PSIG.
No. 14.696 PSI is the standardatmospheric pressure at sea level under defined conditions. Actual atmospheric pressure varies with altitude, temperature, and weather. At 5,000 feet elevation, atmospheric pressure is approximately 12.23 PSI — about 17% lower than sea level.
Both ATM and PSIA are absolute pressure units referenced to a perfect vacuum. 1 ATM equals 14.6959 PSIA. The difference is the unit: ATM is used in scientific contexts while PSIA is used in U.S. engineering. Neither is gauge pressure — they both include the atmospheric baseline in their measurement.
Hydraulic hose working pressure ratings are in gauge pressure (PSIG) — pressure above atmospheric. Understanding that 1 ATM = 14.696 PSI helps technicians correctly convert absolute-pressure specifications from equipment manuals into gauge pressure values that can be compared against hose ratings. Always confirm whether a pressure specification is gauge or absolute before selecting components.
2 ATM equals 29.39 PSIA(2 × 14.6959) or approximately 14.69 PSIG(29.39 − 14.696). 2 ATM is roughly the pressure at 33 feet underwater and approximately double sea-level atmospheric pressure.
Lower atmospheric pressure at altitude reduces the absolute pressure of compressed air systems at the same gauge reading. For compressed air, this affects available air density and system performance. For pump systems, lower atmospheric pressure reduces the available NPSH (net positive suction head), increasing the risk of cavitation. System designers working at significant elevation should account for local atmospheric pressure in calculations.