Sevens of SI (Système International d’unités)

Formerly known as the Metric System

• Seven Base Units of SI
• Seven Definitional Constants of SI

Seven Base Units of SI

Seven Definitional Constants of SI

• Δν_Cs = hyperfine transition frequency of Cesium = 9,192,631,770 s⁻¹ (defines the second)
• c = speed of light in a vacuum = 299,792,458 m/s (defines the meter)
• h = Planck constant = 6.62607015×10⁻³⁴ J⋅s (defines the kilogram: 1 J = 1 kg⋅m²⋅s⁻¹)
• e = elementary charge = 1.602176634×10⁻¹⁹ C (defines the Ampere: 1 A = 1 C·s⁻¹)
• k = Boltzmann constant = 1.380649×10⁻²³ J·K⁻¹ (defines the Kelvin)
• N_A = Avogadro constant = 6.02214076×10²³ mol⁻¹ (defines the mole)
• K_cd = luminous efficacy of 540 THz radiation = 683 lm·W⁻¹ (defines the candela: 1 lm = cd⋅sr, where sr = steradian)

Notes:

• A sphere has a solid angle of 4π sr
• The Watt is defined as 1 W = 1 J/s = 1 kg⋅m²⋅s^-3