# Standard Units for Measurements in Electrical and Electronics Engineering

In the standard units of electrical measurement voltage is measured in volts (V) current in ampere (A) and resistance in Ohm (Ω). These units used in electrical measurement are referred to as the International (metric) System, also known as the SI System with other commonly used electrical units being derived from SI base units.

It is however necessary in some situations to use multiples or sub-multiples (fractions) of these standards electrical measuring units when the quantities being measured are very large or very small (depending on the value being measured).

The table below shows some of the standard electrical units of measure used in electrical formulas and component values.

Standard Units in Electrical Measurement

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 Electrical Parameter Measuring Unit Symbol Description Voltage Volt V or E Unit of Electrical Potential V = I × R Current Ampere I or i Unit of Electrical Current I = V ÷ R Resistance Ohm R or Ω Unit of DC Resistance R = V ÷ I Conductance Siemen G or ℧ Reciprocal of Resistance G = 1 ÷ R Capacitance Farad C Unit of Capacitance C = Q ÷ V Charge Coulomb Q Unit of Electrical Charge Q = C × V Inductance Henry L or H Unit of Inductance VL = -L(di/dt) Power Watts W Unit of Power P = V × I  or  I2 × R Impedance Ohm Z Unit of AC Resistance Z2 = R2 + X2 Frequency Hertz Hz Unit of Frequency ƒ = 1 ÷ T

### Multiples and Sub-multiples

In electrical and electronic engineering analysis and calculations, there is a huge range of values encountered between a maximum value and a minimum value of a standard electrical unit. By making use of the multiples and submultiples of the standard unit we save ourselves the trouble of writing too many zeros to define the position of the decimal point. The table below gives their names and abbreviations.

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 Prefix Symbol Multiplier Power of ten Terra T 1,000,000,000,000 1012 Giga G 1,000,000,000 109 Mega M 1,000,000 106 kilo k 1,000 103 none none 1 10 centi c 1/100 10-2 milli m 1/1,000 10-3 micro µ 1/1,000,000 10-6 nano n 1/1,000,000,000 10-9 pico p 1/1,000,000,000,000 10-12

More insight into the use of multiples and sub-multiples

• 1kV (1 kilo-volt)is equal to 1,000 Volts.
• 1mA (1 milli-amp) is equal to one thousandths (1/1000) of an Ampere.
• 1kΩ (kilo-ohms) is equal to 1000 Ohms.
• 1uF (1micro-farads) is equal to 1 millionths (1/1,000,000) of a Farad.
• 1kW (1 kilo-watt) is equal to 1,000 Watts.
• 1MHz (1 mega-hertz) is equal to one million Hertz.