What Is Voltage?

Voltage is the electrical potential difference between two points in a circuit. It's the "push" or "pressure" that moves electrons; its unit is the volt (V). Without voltage, current doesn't flow.

Voltage = Potential Difference

Voltage is always defined between two points; "the voltage at a single point" only makes sense relative to a reference (usually ground/GND). A battery being "1.5 V" means the potential difference between its two terminals is 1.5 volts.

The Water-Pipe Analogy

The easiest way to understand voltage is plumbing: voltage is the water pressure, current the amount of water through the pipe, and resistance the narrowness of the pipe. The higher the pressure (voltage), the more water (current) flows through the same pipe.

Unit and Multiples

Voltage Sources

Batteries, adapters, USB ports and power supplies are all voltage sources. Sources can be DC (constant, e.g. a battery) or AC (varying, e.g. the mains); for details see The Difference Between AC and DC.

How Is Voltage Measured?

Voltage is measured by connecting the multimeter in parallel to the two points to be measured (unlike current). The range is set to V⎓ for DC and V∼ for AC.

Common Mistakes

• Looking for a single-point voltage: voltage is always between two points; without a reference (GND) the measurement is meaningless.
• Mixing up AC/DC ranges: the wrong range gives a wrong reading.
• Confusing voltage with current: voltage is the "push," current is the amount of "flow."