Engineering Constants
Defined and measured constants used in engineering analysis: gravitational acceleration, atmospheric pressure, gas constant, SI prefixes and mathematical constants.
Article 12.01Engineering Constants3 min read
constantsgravityatmospheregas constantSI prefixesmathematicalpieuler
Defined Constants
| Constant | Symbol | Value | Units | Status |
|---|
| Standard gravity | g₀ | 9.80665 | m/s² | Defined (exact) |
| Standard atmosphere | atm | 101325 | Pa | Defined (exact) |
| Speed of light (vacuum) | c | 299792458 | m/s | Defined (exact) |
| Universal gas constant | R | 8.31446 | J/(mol·K) | Defined (exact) |
| Avogadro number | N_A | 6.02214 × 10²³ | 1/mol | Defined (exact) |
| Boltzmann constant | k_B | 1.38065 × 10⁻²³ | J/K | Defined (exact) |
| Stefan-Boltzmann | σ | 5.67037 × 10⁻⁸ | W/(m²·K⁴) | Defined (exact) |
Environment-Dependent Values
The speed of sound is not a universal constant — it depends on the medium and temperature. In air, c = √(γRT) where γ = 1.4, R = 287 J/(kg·K), T = temperature in K. Do not present the speed of sound as one fixed value without stating the conditions.
| Property | Typical Value | Units | Notes |
|---|
| Air density (sea level, 15°C) | 1.225 | kg/m³ | ISA condition |
| Speed of sound (sea level, 15°C) | 340.3 | m/s | ISA condition; depends on temperature |
| Air viscosity (15°C) | 1.789 × 10⁻⁵ | Pa·s | Dynamic |
| Water density (4°C) | 1000 | kg/m³ | |
| Water density (20°C) | 998 | kg/m³ | |
SI Prefixes
| Prefix | Symbol | Factor |
|---|
| giga | G | 10⁹ |
| mega | M | 10⁶ |
| kilo | k | 10³ |
| milli | m | 10⁻³ |
| micro | μ | 10⁻⁶ |
| nano | n | 10⁻⁹ |
Mathematical Constants
| Constant | Symbol | Value |
|---|
| Pi | π | 3.14159 26535 |
| Euler's number | e | 2.71828 18285 |
| √2 | — | 1.41421 35624 |
| √3 | — | 1.73205 08076 |
| ln(10) | — | 2.30258 50930 |
Notes
- Defined constants are exact by convention — they have no uncertainty
- Environment-dependent values vary with temperature, pressure and composition
- g₀ = 9.80665 m/s² is the standard reference value — local gravity varies slightly with latitude and altitude
- Always state the conditions when quoting an environment-dependent value
Related Knowledge
See Units and Conversions for engineering unit conversion factors.