Last updated: October 2026

To use a multimeter, plug the black lead into COM, plug the red lead into the jack that matches what you are measuring, turn the dial to that function, and touch the probes to the circuit. Voltage is measured across two points with the circuit powered, resistance and continuity are measured with power off, and current is measured in series by breaking the circuit. This guide walks through each mode using batteries, resistors, LEDs and breadboard circuits only.

Safety scope: everything here is low-voltage bench work: batteries, breadboards and bench power supplies. Measuring household mains is a job for a licensed electrician with a CAT-rated meter. Follow your meter maker’s manual for anything beyond this page.

Step 1: Learn the dial, jacks and buttons

Fluke’s guide to multimeter symbols lists the functions you will see on most dials: AC voltage (a wavy line next to V), DC voltage (a solid line over a dashed line), millivolts (mV), resistance (Ω), continuity (a sound-wave symbol), diode test (an arrow pointing at a bar), capacitance (F) and current in amps, milliamps and microamps.

The jacks matter as much as the dial. Per Fluke:

  • COM takes the black lead for every measurement.
  • V/Ω takes the red lead for voltage, resistance, diode, capacitance, temperature and frequency.
  • A takes the red lead for current up to 10 A.
  • mA/µA (on some models) takes the red lead for small currents, 0 to 400 mA on the meters Fluke describes.

Fluke’s rule is worth memorising: the jack chosen for the red lead must match the function selected on the dial.

Common buttons include HOLD (freezes the reading), REL (stores a reference and shows the difference) and RANGE (covered in Step 7).

Step 2: Measure DC voltage

DC voltage is the reading you will take most often on a bench: battery health, a 5 V rail on a breadboard, the output of a bench supply.

  1. Turn the dial to DC voltage (V with the solid line). If your meter also has a DC millivolt position and you are unsure which to use, Fluke recommends starting with DC volts, which handles the higher voltage.
  2. Plug the black probe into COM and the red probe into V/Ω.
  3. Touch the black probe to the negative side or circuit ground and the red probe to the positive point. For a AA cell, that is the flat end and the button end.
  4. Read the display.

If the reading shows a minus sign, the probes are reversed. Fluke notes that modern digital meters detect polarity automatically, so this does no harm; the meter simply shows a negative value. If the reading is very small, Fluke suggests disconnecting, switching to the DC millivolt position and reconnecting.

When you finish, Fluke recommends removing the probes in reverse order: red first, then black.

The one mistake to avoid: Fluke warns that leaving the red lead in the A or mA jack while measuring voltage creates a short through the meter. Always check the red lead’s jack before touching a powered circuit.

Step 3: Measure resistance

  1. Remove power from the circuit. Fluke also says to discharge any capacitor in the circuit before measuring resistance.
  2. Turn the dial to Ω.
  3. Black lead in COM, red lead in V/Ω.
  4. With the probes apart, the display reads OL (overload). Fluke explains that this is normal, because open leads have very high resistance.
  5. Touch the probes across the resistor and read the value.

Tips from Fluke’s resistance guide:

  • Touch the probe tips together first. The display should read close to 0 Ω. For low-value parts, use REL mode to subtract the lead resistance.
  • Do not hold both metal probe tips with your fingers. Your body becomes a parallel resistance and lowers the reading.
  • For the most accurate result, measure the component out of the circuit. Other parts connected in parallel change the reading.

On a manual-ranging meter, SparkFun’s tutorial advises starting on a high range. If the display shows “1” or OL, the value is above that range, so move up; if it shows 0.00, move down.

Step 4: Test continuity

Continuity tells you whether two points are connected: a wire, a fuse, a switch, a PCB trace.

  1. Power off the circuit.
  2. Turn the dial to continuity. Fluke notes it often shares a position with Ω, and some meters need a button press to switch into continuity.
  3. Black lead in COM, red lead in V/Ω.
  4. Touch the probes to each end of the path. The meter beeps if the path is complete.

Fluke gives an example threshold: on a 400.0 Ω range, a meter typically beeps at 40 Ω or less. The exact threshold varies by model, so check your manual. Make sure the part is isolated from other components, or the beep may come from a parallel path.

For a deeper walk-through of fuses and switches, see testing continuity, fuses and diodes.

Step 5: Use the diode test

The diode mode pushes a small current through the part and shows the voltage drop.

  1. Power off the circuit and discharge any capacitors, as Fluke instructs.
  2. Turn the dial to the diode symbol.
  3. Touch the red probe to the anode and the black probe to the cathode (the end with the stripe). Record the reading.
  4. Reverse the probes and record again.

What Fluke says the readings mean for common silicon diodes:

ResultForward (red on anode)Reverse (red on cathode)
Good diodeabout 0.5 to 0.8 VOL
Open diodeOLOL
Shorted diodeabout 0.4 Vabout 0.4 V

Step 6: Measure current (and protect the fuse)

Current is the mode most likely to blow a fuse, because the meter must become part of the circuit.

  1. Turn off the circuit’s power.
  2. Move the red lead to a current jack. SparkFun suggests starting with the fused low-current jack (200 mA on the meter in their tutorial) for typical breadboard projects, and moving to the 10 A jack if you expect more.
  3. Turn the dial to DC current (mA or A to match the jack).
  4. Break the circuit at one point, for example by pulling one leg of a resistor out of the breadboard row. SparkFun puts it simply: you have to interrupt the flow of current and put the meter in line.
  5. Connect the meter across the gap so current flows in through one probe and out through the other. The meter is now in series.
  6. Restore power and read the display.

Two fuse warnings from SparkFun’s tutorial:

  • Overloading a current range can blow the meter’s fuse rather than just show an overload message.
  • If a fuse blows, replace it with the same rating. Never put a 10 A fuse where a 200 mA fuse belongs.

When you finish, move the red lead back to V/Ω and the dial back to voltage. SparkFun recommends this every time, because the next person to pick up the meter will probably measure voltage, and Fluke warns that measuring voltage through a current jack creates a short.

Never place the meter in current mode directly across a battery or power supply. A meter set up for current is meant to sit in line like a wire, so putting it across a source is the same short circuit Fluke warns about.

Step 7: Understand auto-ranging vs manual ranging

An auto-ranging meter picks the scale for you. According to Fluke’s description of the RANGE button, the meter starts in autorange; pressing RANGE switches to manual mode and steps through the ranges, and holding RANGE for about two seconds returns to autorange (on the meters Fluke documents; check your manual).

A manual-ranging meter has several positions per function, such as 2 V, 20 V and 200 V. SparkFun’s rule: pick the lowest range that is still higher than what you expect. Their examples: a 12 V battery or a 5 V system both go on the 20 V range. If you do not know the value, start at the highest range and work down. A “1” or OL means the value is above the selected range.

Auto-ranging is easier to learn on. Manual ranging can be faster when you are measuring many similar values, because the meter does not have to settle on a new range each time.

Practice routine

  • Measure a fresh AA cell and a used one on DC volts.
  • Measure three resistors from a kit and compare them to their color bands.
  • Check continuity across a jumper wire, then across a gap in a breadboard row.
  • Diode-test a 1N4148 or 1N4001 in both directions.
  • Measure the current through an LED and resistor on a 5 V breadboard rail.

When you are ready to buy a better meter, see the electronics multimeter guide and the multimeter spec table. To check capacitors, continue with how to test a capacitor.

FAQ

Which jack does the red lead go in for voltage? The V/Ω jack. The A and mA jacks are only for current, and measuring voltage through them creates a short, according to Fluke.

Why does my meter show OL? On resistance, OL with the probes apart is normal. On any function, OL or “1” means the value is above the current range. Move to a higher range or let auto-ranging settle.

Why did my meter stop reading current? The most common cause is a blown current-range fuse, often from measuring voltage with the red lead still in a current jack. Replace it with the exact rating your manual specifies.

Do I need a true-RMS meter for electronics? Not for DC work on batteries and breadboards. True-RMS matters for AC waveforms that are not clean sine waves. See the electrician meter guide for how makers describe it.

Can I measure an outlet with this method? No. This guide covers low-voltage bench work only. Mains measurements belong to qualified people using CAT-rated gear and the maker’s manual.

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