EngiRef / Collection
Constants
Scientific constants
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All Constants
Scientific constants
Speed of Light in Vacuum
Exact defined value in SI. Maximum speed in universe.
Planck Constant
Exact defined value in SI. Relates photon energy to frequency.
Reduced Planck Constant
h/(2π). Common in quantum mechanics.
Elementary Charge
Exact defined value in SI. Charge of a proton.
Avogadro's Constant
Exact defined value in SI. Particles per mole.
Gravitational Constant
Universal gravitation constant. F = GMm/r².
Fine Structure Constant
Dimensionless. Characterizes electromagnetic interaction strength.
Vacuum Permittivity
Electric constant. Appears in Coulomb's law.
Vacuum Permeability
Magnetic constant. Since the 2019 SI redefinition μ₀ is a measured quantity; 4π × 10⁻⁷ H/m is the pre-2019 exact value and now differs in the 10th digit.
Coulomb Constant
1/(4πε₀). Force between point charges.
Faraday Constant
Charge per mole of electrons. F = Nᴀ × e.
Boltzmann Constant
Exact defined value in SI. Relates temperature to energy.
Molar Gas Constant
Universal gas constant. R = Nᴀ × k.
Stefan-Boltzmann Constant
Blackbody radiation. P = σAT⁴.
Standard Atmosphere
Standard atmospheric pressure at sea level.
Gas Constant for Air
Specific gas constant for dry air.
Standard Gravity
Standard acceleration due to gravity on Earth.
Standard Gravity (Imperial)
Standard gravity in imperial units.
Electron Mass
Rest mass of an electron.
Proton Mass
Rest mass of a proton.
Neutron Mass
Rest mass of a neutron.
Atomic Mass Unit
Unified atomic mass unit. 1/12 mass of ¹²C.
Bohr Radius
Most probable distance of electron from nucleus in hydrogen.
Density of Water (20°C)
Fresh water density at 20°C and 1 atm.
Density of Air (ISA sea level)
Dry air at 15°C and 101.325 kPa (ISA sea level). Note this is the ISA reference condition, not STP; dry air at 0°C and 101.325 kPa is 1.2754 kg/m³.
Specific Heat of Water
Specific heat capacity of liquid water near 15°C (the calorie-defining condition). At 25°C the value is about 4180 J/(kg·K).
Dynamic Viscosity of Water (20°C)
Dynamic viscosity of water at 20°C.
Dynamic Viscosity of Air (20°C)
Dynamic viscosity of air at 20°C and 1 atm.