How to use a multimeter to measure voltage and current in a circuit?

A multimeter is an instrument for measuring voltage, current or resistance.

It can tell you the values of different components and what’s going on in different parts of your circuit. Since you can’t see what’s going on inside a circuit or component, a multimeter is essential for understanding its inner workings.

Why use a multimeter?

In a circuit, you may have theoretically calculated the volts, amperes and resistance required for its correct operation. In real life, however, there are factors that cannot be anticipated. If one of your components fails, it can take hours to figure out where the problem lies, and the multimeter will save you a lot of time!

How does a multimeter work?

The multimeter is made up of several parts, which we’ll describe below to help you understand how to use it.

  • Digital display: The multimeter’s digital display shows the number measured by the multimeter.
  • Mode selection wheel: This wheel lets you choose between the different functions offered by the multimeter. If you want to measure voltage, current or resistance, you won’t choose the same multimeter function.
  • Two probes: Two probes are supplied with your multimeter to take your measurements. These probes are usually red and black, and are placed in your circuit between the components you wish to measure.
  • The 3 sockets: A multimeter often has three sockets: a COM socket is the multimeter’s ground. The black probe is connected to this. A V socket is the Vcc, where the red probe is usually plugged in. Finally, the last socket is used to test whether the multimeter is indicating the correct value. In fact, a value is written on this terminal and the multimeter is supposed to display the same value when the probe is connected to it.


Alligator sockets can be very useful in a circuit for securing probes, so you don’t have to hold them while taking measurements. They can also free up your hands for other manipulations (without power, of course!).

How do you always read a positive value?

When measuring a value, it may be negative. This is not serious, the value is correct, but the problem is that the red and black probes have been reversed in the circuit measurement. In fact, to get a positive value, you should always put the red probe on the positive side of your circuit and the black probe on the negative side.

Measuring voltage in a circuit

Measuring voltage is very useful in a project to measure the voltage of a battery or the current flowing through a component. Voltage is measured in volts.

To measure voltage, you first need to make sure that the probes are plugged into the right sockets. These sockets should be labelled V for volts in the case of the red probe, and COM for ground in the case of the black probe.

You also need to turn the dial to direct current (DC), which can be represented by a V sign with a line above it.

How is voltage measured?

Voltage is measured in parallel, which means you need to position yourself on either side of the part of the circuit whose voltage you want to measure.

Here’s an example just below, with an LED and a resistor:

Measuring current in a circuit

You may have the right voltage but not enough current to light a led, for example. In this case, you need to change the dial to the correct rating: A,mA (milli-Ampere) or ⴗA (micro-Ampere).

How is intensity measured?

Intensity is measured in series, i.e. the multimeter must be placed in the continuity of the components, as if the multimeter were one more component in your circuit.

Here’s an example just below:

The value of a resistor

The multimeter can also be used to measure the value of a resistor.

We’ve done a course to determine the value with the colors of the bands and we have an Arduino factory application that gives the value of the resistor.

However, if the resistance bands are a little faded, you can use a multimeter to determine its value.

To do this, set the knob to ohm or Ω and place a probe on each resistor leg.

Here’s an example just below:

Circuit continuity

Some multimeters have a continuity function. You can see it on the thumbwheel, a function characterized by a loudspeaker symbol.

It’s a continuity tester that lets you test your circuit to see if there’s a burnt-out component or a disconnected wire. The multimeter will send a small current to the red probe, and if the black probe receives the small current, then the circuit is closed and the multimeter will beep.

Here’s an example:

Circuit supply

When testing continuity, always disconnect all power sources connected to your circuit to avoid false beeps.