Constants & SI system

• cSpeed of light in vacuumNothing is faster. The metre is defined from it.299,792,458 (exact)m/s
• gStandard gravityHow much falling objects on Earth speed up each second.9.80665m/s²
• GGravitational constantSets how strongly masses attract each other.6.674 × 10⁻¹¹m³/(kg·s²)
• hPlanck constantThe smallest portion of action, the heart of quantum physics.6.626 070 15 × 10⁻³⁴ (exact)J·s
• eElementary chargeThe charge of a single proton, electrons carry −e.1.602 176 634 × 10⁻¹⁹ (exact)C
• mₑElectron massAbout 1836 times lighter than a proton.9.109 × 10⁻³¹kg
• uAtomic mass unitHandy unit for atomic masses, roughly one proton.1.660 539 × 10⁻²⁷kg
• NₐAvogadro constantThat many particles make up one mole.6.022 140 76 × 10²³ (exact)1/mol
• k_BBoltzmann constantTranslates temperature into particle energy.1.380 649 × 10⁻²³ (exact)J/K
• RUniversal gas constantLinks pressure, volume and temperature of gases.8.314 462 618J/(mol·K)
• 0 KAbsolute zeroIt cannot get colder, particle motion is at its minimum.−273.15°C

• AEAstronomical unitThe mean Earth-Sun distance, the ruler of the solar system.149.6 millionkm
• LjLight yearThe distance light travels in one year.9.46 trillionkm
• –Earth-Moon distanceOn average, light needs 1.3 seconds for it.384,400km
• R⊕Earth radiusThe mean radius of our planet.6,371km
• M⊕Earth massThe reference mass for rocky planets.5.97 × 10²⁴kg
• M☉Solar massAbout 333,000 Earth masses, the reference mass for stars.1.989 × 10³⁰kg

Seven units that all other units are built from.

Named units built from the base units.

Prefixes turn a unit into a multiple or a fraction.