Resistors are fundamental electronic components that play a crucial role in electrical circuits. Whether you're a beginner exploring the world of electronics or an experienced engineer seeking detailed information, this page aims to provide you with comprehensive insights into resistors and their applications.

What is a Resistor?

A resistor is an electrical component designed to impede the flow of electric current within a circuit. It is specifically constructed to provide a specific amount of electrical resistance to the flow of electrons. Resistance is measured in ohms (Ω) and is denoted by the symbol "R."

They are passive components, meaning they only consume power (and can’t generate it). 

Resistors are usually added to circuits where they complement active components like op-amps, microcontrollers, and other integrated circuits. Commonly resistors are used to limit current,  and divide voltages.

Understanding Resistance

Resistance is a property of materials that determines how easily they allow the passage of electric current. Materials with high resistance impede the flow of electrons, while those with low resistance allow for easier flow. The resistance of a material depends on factors such as its length, cross-sectional area, and resistivity. See our Ohm's Law and Resistance Pages for more information on this. 

Resistor Units

The electrical resistance of a resistor is measured in ohms. The symbol for an ohm is the greek capital-omega: Ω. 

The definition of 1Ω is the resistance between two points where 1 volt (1V) of applied potential energy will push 1 ampere (1A) of current.

As SI units go, larger or smaller values of ohms can be matched with a prefix like kilo-, mega-, or giga-, to make large values easier to read. 

-It’s very common to see resistors in the kilohm (kΩ) and megaohm (MΩ) range 

-For example, a 4,700Ω resistor is equivalent to a 4.7kΩ resistor, and a 5,600,000Ω resistor can be written as 5,600kΩ or (more commonly as) 5.6MΩ.

Schematic Symbol

All resistors have two terminals, one connection on each end of the resistor. When modeled on a schematic, a resistor will show up as one of the two symbols on the right below. Note how they look similar to the through-hole resistor image on the left.

Types of Resistors

Resistors come in a variety of shapes and sizes. They might be through-hole or surface-mount. They might be a standard, static resistor, a pack of resistors, or a special variable resistor.


Through-hole resistors come with long, pliable leads which can be stuck into a breadboard or hand-soldered into a prototyping board or printed circuit board (PCB). 

Surface Mount

Surface-mount resistors are usually tiny black rectangles, terminated on either side with even smaller, shiny, silver, conductive edges. These resistors are intended to sit on top of PCBs, where they’re soldered onto mating landing pads. Because these resistors are so small, they’re usually set into place by a robot, and sent through an oven where solder melts and holds them in place.

Resistor Composition

Resistors can be constructed out of a variety of materials. Most common, modern resistors are made out of either a carbon, metal, or metal-oxide film. In these resistors, a thin film of conductive (though still resistive) material is wrapped in a helix around and covered by an insulating material. Most of the standard, no-frills, through-hole resistors will come in a carbon-film or metal-film composition.

Reading Resistor Color Bands

Through-hole, axial resistors usually use the color-band system to display their value. Most of these resistors will have four bands of color circling the resistor.

The first two bands indicate the two most significant digits of the resistor’s value. 

The third band is a weight value, which multiplies the two significant digits by a power of ten.

The final band indicates the tolerance of the resistor. The tolerance explains how much more or less the actual resistance of the resistor can be compared to what its nominal value is. No resistor is made to perfection.

What is this resistor’s value?

Yellow: 4     Violet: 7     Red: 102 or 100     Gold: +-5%     

Sooo.. 4700Ω or 4.7KΩ +- 235Ω 

For more information on Resistors and a few experiments to build to further understand them, check out our page on Resistors in a Circuit.

Will's Resistor Chart

Will's Resistor Chart is a digital resistor color code identifier made by a MakerLesson's student. First, click on the number of digits corresponding to the number of bands on the resistor you are trying to measure. Then click the corresponding color bands for the digits, multiplier, and tolerance bands. Your resistor value will show below in Ohms. 

Applications of Resistors

Voltage Dividers

Resistors are used to divide voltages in circuits, allowing the creation of specific voltage levels.

Current Limiting

They are employed to control the amount of current flowing through various components, protecting them from damage.

Signal Conditioning

Resistors are used to modify and adjust electrical signals to match the requirements of different components or circuits.

Timing Circuits

They play a vital role in timing circuits, determining the duration and frequency of electronic signals.