What Is a Multimeter, and How Do You Use It?

A multimeter is the basic measuring instrument that anyone working with electronics should own — it can measure many electrical quantities in a single device, such as voltage, current, resistance and continuity.

What Does a Multimeter Measure?

• Voltage (V): DC and AC volts
• Current (A): the current through the circuit
• Resistance (Ω): a component's resistance
• Continuity: whether two points are connected (audible beep)
• Most models also have diode test and capacitance

How Is Voltage Measured?

Set the range to V (V⎓ for DC, V∼ for AC) and connect the probes in parallel to the points you're measuring. The black probe should be in COM, the red probe in the VΩ input. For example, touch a battery's terminals and you read 1.5 V.

How Is Current Measured?

To measure current, the multimeter is connected in series with the circuit; that is, you break the circuit and pass the current through the multimeter. Don't forget to plug the red probe into the A (current) input, which is separate on most meters. Choosing the right jack for high currents protects the fuse.

Resistance and Continuity

When measuring resistance, the component must be out of the circuit (you'll read wrong in-circuit). In continuity mode the meter beeps if two points are connected — the fastest way to find a broken wire or a short.

Common Mistakes

• Connecting in parallel in current mode: the most common and most expensive mistake — the multimeter acts like a short and blows its fuse. Current is always measured in series.
• Wrong range: on meters without auto-ranging, it's safe to pick a larger range than expected and work down.
• Measuring resistance in-circuit: other components corrupt the result.