Basic Electronic Formulas

Basic electronic formulas are included to aid you in solving electrical problems. These formulas are for capacitance, current, inductance, power, reactance, impedance, resistance, voltage, and transformers.

In order to perform simple to complex calculations in electronics you must know what formulas to use and how to apply them. Without this basic knowledge on how to perform these simple functions you will not be able to determine voltage, current, resistance, power and many other important factors related to electronics and electricity.

We will present a few of the basic formulas for capacitance in this tutorial.


The property of an electrical device to store energy is CAPACITANCE. This energy is stored in a way to oppose a change in voltage.

A CAPACITOR is used to store this electrical energy. The FARADis the basic unit of measurement of capacitance.

Basic electronic formulas for capacitance:

Common insulating materials for capacitors and their dielectric constant are:


Vacuum 1.0000

Air 1.0006

Paraffin paper 3.5

Glass 5 to 10

Mica 3 to 6

Rubber 2.5 to 35

Wood 2.5 to 8

Glycerine (15º C) 56

Petroleum 2

Pure Water 81

The time to charge a capacitor to 63.2 percent of applied voltage or discharge it to 36.8 percent of its initial voltage is known as the TIME CONSTANT (t) of the circuit. The picture below shows an RC time constant chart. One time constant (t) in seconds equals R × C, with R in ohms and C in farads.

RC Time Constant Chart

The next picture is a universal time constant chart for RC and LR circuits. One time constant (t) in seconds equals R × C, with R in ohms and C in farads, or L/R with L in henries and R in ohms.

Time in time constants chart.

Adding capacitors in series:

If only two capacitors are used:

If more than two capacitors are used:


Capacitors retain an electrical charge. Be sure to discharge all capacitors and circuits containing capacitors before working on them.

Formulas for Current

Formulas for Inductance

Formulas for Power

Reactance Formulas and More

Antenna Formulas and Resonance

Transistor Formulas

Vacuum Tubes and Wavelength Formulas

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