Resistors restrict or limit the flow of current in a circuit. The ability of a material or component to resist current flow is measured in ohms. There are three main types of resistor:

fixed resistors

Fixed: These are the most common type of resistor. They have three important uses: protecting components, dividing voltage between different parts of a circuit and controlling a time delay.

variable resistors

Variable: These are resistors that are continually alter when in use.  These are used in volume control on radio for example. Potentiometer (voltage dividers), Rheostat (to control the resistance with in the circuit), Trimpot (also known as a preset: it is a miniature adjustable electrical component. It is meant to be set correctly when installed in ‘a’ device, and never seen or adjusted by the device’s user)

special resistors

Special:  These are resistor that respond to temperature (Thermal) for light (Light dependent). They by having a photo-sensitive area that reacts to light levels. Types of special resistors include thermistors and light-dependent resistors (LDRs)

Colour Codes of Resistors

Colour band on resistor

Colour band on resistor

The “left-hand” or the most significant coloured band is the band which is nearest to a connecting lead with the colour coded bands being read from left-to-right as follows for the above image;

Digit, Digit, Multiplier = Color Colour x 10colour  in Ohm’s (Ω’s) 

Yellow Violet Red = 2 7 0 = 2 7 x 105 = 2700Ω or 2k7.

Not sure what resistor you need or what is the value of the ones that you have, then try this very useful online calculator to work it out.

Tolerance: The tolerance of a resistor is the maximum difference between its actual value and the required value and is generally expressed as a plus or minus percentage value. This is usually the fourth and Fifth bands on the resistor. If there are only 3 bands then the tolerance is 20%.  Other coloured bands have the following values Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 %. (Gold and Silver are sometimes replaced for non metal paints). The lower the tolerance the more expensive the resistor is.