Standard atmosphere reference
Standard Sea-Level Conditions
Reference the core International Standard Atmosphere sea-level values used in aerospace, HVAC, thermodynamics, and fluid mechanics calculations.
Sea-level reference values
Standard atmosphere at 0 m altitude
Use these values as common baseline inputs for early engineering calculations and model checks.
Core constants
Dry air at sea level
1.225 kg/m3
At 15 °C and 101.325 kPa
Reference table
Standard sea-level atmospheric properties
| Property | SI Value | Imperial / Alternate Value | Common Use |
|---|---|---|---|
| Temperature | 288.15 K / 15 °C | 59 °F | Thermal and atmosphere reference |
| Pressure | 101.325 kPa | 14.696 psi / 1 atm | Barometric and gas-law calculations |
| Density | 1.225 kg/m3 | 0.0765 lb/ft3 | Lift, drag, mass flow, buoyancy |
| Specific Gas Constant | 287.05 J/(kg.K) | 1716 ft.lbf/(slug.deg R) | Ideal gas law for dry air |
| Gravity | 9.80665 m/s2 | 32.174 ft/s2 | Weight, hydrostatics, dynamics |
| Speed of Sound | 340.3 m/s | 1116 ft/s | Mach number and compressible flow |
| Dynamic Viscosity | 1.789 x 10-5 Pa.s | 3.737 x 10-7 slug/(ft.s) | Reynolds number and shear flow |
Formulas
Common sea-level atmosphere formulas
Ideal gas law
ρ = p / (R x T)
p = 101,325 Pa
T = 288.15 K
Speed of sound
a = sqrt(gamma x R x T)
gamma = 1.4 for dry air
R = 287.05 J/(kg.K)
Standard sea-level values are reference values for dry air. Real conditions vary with weather, humidity, elevation, and temperature, so use measured local data for final design calculations.
Reference
How engineers use sea-level conditions
Aerospace
Sea-level standard density, pressure, and speed of sound are used for lift, drag, Mach number, engine performance, and test normalization.
HVAC
Air density and specific properties provide baseline assumptions for airflow, ventilation, heating, and cooling calculations.
Fluid mechanics
Density and viscosity support Reynolds number, pressure drop, fan, duct, and aerodynamic force checks.
Thermodynamics
Temperature, pressure, and gas constant values connect pressure, density, and energy relationships for dry air.
FAQ
Standard sea-level condition questions
What are standard sea-level conditions?
Standard sea-level conditions are reference atmospheric values at mean sea level, commonly including 15 degrees C, 101.325 kPa, and 1.225 kg/m3 for dry air.
What is standard sea-level air density?
Standard sea-level dry-air density is approximately 1.225 kg/m3, or 0.0765 lb/ft3.
Are standard sea-level values the same as local weather?
No. Standard sea-level values are reference conditions; actual weather pressure, temperature, humidity, and density vary.
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