# Common Units and Prefixes used in Physical Systems

Contents

## Units

The following table contains the fundamental units for various types of systems.  See also the page at the NIST (National Institute of Standards and Technology) website.  Each unit is written out, followed by its abbreviation in parentheses, ().  If other equivalent forms of the unit are commonly used, they are given in brackets, [].  Both SI (from French for "Le Système International d'Unités") and English units are given.

 Fundamental Quantities SI unit English Unit Conversion Time second (s) second (s) Mass kilogram (kg) slug 1 slug = 14.6 kg Length meter (m) foot (ft) 1 ft = 0.305 m Force Newton (N) pound (lb) 1 lb = 4.45 N Energy Joule (J) [W-s, N-m] foot-pound (ft-lb)British Thermal Unit (BTU) 1 ft-lb = 1.36 J1 BTU = 1055 J Power Watt (W) [J/s] horsepower (hp) 1 hp = 746 W Moment of intertia (kg-m²) (slug-ft²) 1 slug-ft² = 1.36 N-m² Torque Newton-meter (N-m) foot-pound (ft-lb) 1 ft-lb = 1.36 N-m Voltage Volt (V) Volts (V) Charge Coulomb (C) Coulomb (C) Current Amperes (A=C/s) Amperes (A) Absolute Temperature Degrees Kelvin (°K) Degrees Rankine (°R) 1 °R = 9/5 °K CommonTemperatureScales Degrees Celsius (°C) Degrees Fahrenheit (°F) °F = °Cx9/5+32°C = °K-273.15°F = °R-459.67 Linear Mechanical Systems Spring Constant (N/m) (lb/ft) Friction Coefficient (N-s/m) (lb-s/ft) Rotating Mechanical Systems Spring Constant (N-m/rad) (ft-lb/rad) Friction Coeffiicient (N-m-s/rad) (ft-lb-s/rad) Thermal Systems Thermal Resistance °K/W s-°R/BTU Thermal Conductance W/°K BTU/(s-°R) Thermal Capacitance, orThermal Mass J/°K BTU/°R Electrical Systems Electrical Resistance Ohm-Ω (V/A) Ohm-Ω (V/A) Electrical Conductance Siemens-S (A/V) (Note)  You will sometimes see conductance measured with a unit of a "mho". The word "mho"is the word "ohm" spelled backwards); and the symbol was an upside down Ω (℧) because conductance is the inverse of resistance. Siemens-S (A/V) Capacitance Farad-F (C/V) Farad-F (C/V) Inductance Henry-H (V-s/A) Henry-H (V-s/A)

## Prefixes

The following table gives some of the more common SI prefixes.  If the prefix precedes the name of a unit in the above table, multiply the unit by the prefix multiplier.  For example 4.2 milliAmperes (or 4.2 mA) is 4.2·10-3A (ref with full list).  (note: there is an online effort to have "hella" named as the prefix for 10+27.  It has been adopted by google.)

 Prefix Quantities Symbol Multiplier pico p 10-12 nano n 10-9 micro μ 10-6 milli m 10-3 centi c 10-2 deci d 10-1 kilo k 10+3 mega M 10+6 giga G 10+9 tera T 10+12

References

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