WELLOG                   UNITS OF MEASUREMENT

Revised 11-07-2016

Newtons?          Pascals?            Teslas?

When performing calculations, it is important to decide which system of measurement to use.

Three systems are in use in the world today.

1. Centimeters, Grams, and Seconds (CGS)

1. Meters, Kilograms, and Seconds. (MKS)

1. System International (SI)

Centimeters, Grams, and Seconds (CGS):

This system was introduced in 1874 by the British Association for the advancement of Science. It was and has been used in scientific and engineering applications involving small quantities.

Meters, Kilograms, and Seconds (MKS):

This system was proposed in 1889 by the International Bureau of Weights and Measures (BIPM). Depending on the scale of measurement, scientists and engineers use CGS to measure small quantities and MKS when measuring large quantities.

What happened?

The Tenth General Conference on Weights and Measures (CGPM) adopted MKS as the standard for basic units for all international weights and measures in 1954.

The Eleventh General Conference on Weights and Measures adopted the International System of Units (SI) for this collection of units in 1960.

Today (after year 2000) the only system acceptable for use in testing and measurement is the SI system. Ref: NIST.

System International (SI):

The basic units are…

Mass measured in Kilograms.      kg

Length measured in Meters.        m

Time measured in Seconds.        s

Amount of substance measured in Moles. mol

Electric current measured in Amperes.     A

Thermodynamic temperature measured in Kelvin. K  (not “degrees Kelvin”) Ref CGPM, 1967

Luminous intensity measured in Candela. cd

SI DERIVED UNITS:

Force is measured in Newtons.    N = kg*m/s2

Pressure/stress is measured in Pascals.   Pa = N/m2

Energy or work in Joules.                        J = N * m

Power is measured in watts.       W = J/s

Potential/EMF is measured in volts.                      V = W/A

Magnetic flux is measured in webers.       Wb = V*s

Magnetic flux density is measured in teslas.  T = Wb/m2

Inductance is measured in henrys.           H = Wb/A

Temperature,  measured in Celsius          C = K – 273.15

Electric charge is measured in Coulombs. C = A*S

Resistance is measured in ohms. W = V/A

Conductance is measured in siemens.      S = 1/W

Capacitance is measured in farads.          F = C/V

Frequency is measured in Hertz. Hz = 1/s

Illuminance is measured in lux.    lx = lm/m2

Luminous flux is measured in lumens. Lm = cd*sr

Note: this list is not all inclusive – refer to http://www.physics.nist.gov/ for more units.

WELLOG endorses measurement in SI units. Some text material on this website may reference units not approved or accepted by NIST SI.  Such references are used in text material for clarity and to avoid conflict with earlier established text materials. Conversions are available for conversion of scientific units from unaccepted units to modern accepted SI units.