A voltmeter measures how much voltage is passing between two points. It does this by measuring the difference between the positive input of voltage and the negative input of voltage. A voltmeter is usually used to check the power in electrical circuits.

A voltmeter has three parts you need to know about before you can use it:

  • Positive input terminal (usually red)
  • Negative input terminal (usually black)
  • Display, where you'll see the results of the measurement. If your meter is analog you'll have to read the results from a scale. If it's digital, the results will show up as a reading on an LCD or LED screen [source: Mastascusa].

Before using a voltmeter you'll have to determine whether the current you're measuring is a direct current (that flows in one direction) or an alternating current (that flows back and forth). Make sure you're using a voltmeter that's compatible with the type of current you're measuring, or that your voltmeter is set to the appropriate setting. Turn the dial to select the range of voltage you're measuring [source: Doctronics]. You're now ready to use your voltmeter:

  1. Attach the positive input terminal lead to the positive end of the circuit (or whatever you want to measure the voltage of).
  2. Attach the negative input terminal lead to the negative end of the circuit (or whatever you want to measure the voltage of).

The voltmeter will turn itself on and measure the difference between the voltage at the first point and the voltage at the second point, telling you how much voltage is traveling between the two points [source: Mastascusa].