Constants & units
Constants & units
SI prefixes, base units, frequently used physical constants, and a small conversion table.
SI prefixes
| Prefix | Symbol | Factor |
|---|---|---|
| peta | P | 10¹⁵ |
| tera | T | 10¹² |
| giga | G | 10⁹ |
| mega | M | 10⁶ |
| kilo | k | 10³ |
| hecto | h | 10² |
| deci | d | 10⁻¹ |
| centi | c | 10⁻² |
| milli | m | 10⁻³ |
| micro | μ | 10⁻⁶ |
| nano | n | 10⁻⁹ |
| pico | p | 10⁻¹² |
| femto | f | 10⁻¹⁵ |
| atto | a | 10⁻¹⁸ |
SI base units
| s | second — time |
|---|---|
| m | metre — length |
| kg | kilogram — mass |
| A | ampere — electric current |
| K | kelvin — thermodynamic temperature |
| mol | mole — amount of substance |
| cd | candela — luminous intensity |
Common derived units
| N | newton (kg·m/s² · force) |
|---|---|
| J | joule (N·m · energy) |
| W | watt (J/s · power) |
| Pa | pascal (N/m² · pressure) |
| C | coulomb (A·s · charge) |
| V | volt (J/C · electric potential) |
| Ω | ohm (V/A · resistance) |
| F | farad (C/V · capacitance) |
| H | henry (V·s/A · inductance) |
| Hz | hertz (1/s · frequency) |
| T | tesla (Wb/m² · magnetic flux density) |
| Wb | weber (V·s · magnetic flux) |
| S | siemens (1/Ω · conductance) |
| lm | lumen (cd·sr · luminous flux) |
| lx | lux (lm/m² · illuminance) |
| rad | radian (m/m · plane angle (1)) |
Physical constants
| c | speed of light in vacuum 2.99792458×10⁸ m/s defined (exact) |
|---|---|
| h | Planck constant 6.62607015×10⁻³⁴ J·s defined |
| e | elementary charge 1.602176634×10⁻¹⁹ C defined |
| N_A | Avogadro constant 6.02214076×10²³ mol⁻¹ defined |
| k | Boltzmann constant 1.380649×10⁻²³ J/K defined |
| R | molar gas constant 8.314462618 J·mol⁻¹·K⁻¹ N_A · k (from defined values) |
| G | gravitational constant 6.67430×10⁻¹¹ m³·kg⁻¹·s⁻² CODATA 2018 |
| g | standard gravity 9.80665 m/s² conventional (exact); local g varies |
| ϵ₀ | vacuum permittivity 8.8541878128×10⁻¹² F/m 1/(μ₀ c²). CODATA 2018 |
| μ₀ | vacuum permeability 1.25663706212×10⁻⁶ N·A⁻² measured after 2019 SI. CODATA 2018 |
| σ | Stefan–Boltzmann 5.670374419×10⁻⁸ W·m⁻²·K⁻⁴ blackbody radiation; π² k⁴ / (60 ℏ³ c²) |
| atm | standard atmosphere 101325 Pa defined |
| eV | electronvolt 1.602176634×10⁻¹⁹ J e × 1 V; defined |
| u | atomic mass unit (dalton) 1.66053906660×10⁻²⁷ kg 1/12 of ¹²C. CODATA 2018 |
| α | fine-structure constant 7.2973525693×10⁻³ (≈ 1/137.035999084) e²/(4πϵ₀ ℏ c). CODATA 2018 |
Conversions
| 1 eV | electronvolt to joule 1.602176634×10⁻¹⁹ J defined |
|---|---|
| 1 u | atomic mass unit to kilogram 1.66053906660×10⁻²⁷ kg CODATA 2018 |
| 1 atm | atmosphere to pascal 101325 Pa defined |
| 1 bar | bar to pascal 10⁵ Pa defined |
| 0 °C | Celsius to kelvin 273.15 K T/K = t/°C + 273.15 |
| 1 cal | thermochemical calorie 4.184 J conventional |
| 1 Å | ångström 10⁻¹⁰ m defined |
| 1 ha | hectare 10⁴ m² defined |
| 1 AU | astronomical unit 1.495978707×10¹¹ m defined (2012) |
| 1 ly | light-year 9.4607304725808×10¹⁵ m Julian year × c |
| 1 pc | parsec 3.085677581×10¹⁶ m from AU / tan(1″) |
| 1 hp | metric horsepower 735.49875 W PS; not the 745.7 W mechanical horsepower |
| 1 mi | international mile 1609.344 m defined |
| 1 in | inch 25.4 mm defined |
| 1 kWh | kilowatt-hour 3.6×10⁶ J defined |
| 1 torr | torr 133.322 Pa near 1 mmHg conventional |
| 1 kn | knot 1852 m/h = 0.514444… m/s one nautical mile per hour |
| 1 lb | international pound 0.45359237 kg defined |
| 1 G | gauss to tesla 10⁻⁴ T CGS; 1 T = 10⁴ G |