How to Measure Voltage Across a Resistor with a Multimeter
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How to measure voltage across a resistor with a multimeter is a short job when the steps are done in order. to measure voltage across a resistor with a multimeter, set the meter to DC voltage or AC voltage to match the circuit, put the black lead in COM and the red lead in VΩ, and touch the probes to the two ends of the resistor while the circuit is powered. You do not open the circuit. The meter reads the potential difference between the two points. This guide covers the steps, the polarity rules, and the mistakes that give a wrong reading.
Quick answer
Connect the meter in parallel with the resistor. Select DC volts (⎓) for a DC circuit or AC volts for an AC circuit. Connect black to COM and red to VΩ. Touch black to the negative side of the resistor and red to the positive side, then read the display. A negative sign means the probes are reversed relative to the polarity of the voltage.
Why voltage is measured in parallel
Voltage is the difference in potential between two points, so the meter must connect across the component. A voltmeter has a very high input impedance, which means it draws very little current from the circuit. That is why the resistor stays in the circuit while you measure it. This is the opposite of current measurement, where the meter must be placed in series so the current flows through it.
Fluke describes the DC voltage procedure as touching the black probe to the negative test point and the red probe to the positive test point. Most modern meters show a negative sign when the probes are reversed, so the sign helps confirm which side of the resistor is at the higher potential.
What you need
- A digital multimeter with DC voltage and AC voltage settings. Some meters also have a DC millivolt range for small readings.
- Test leads in good condition and rated for the voltage you will measure. Fluke recommends checking leads for condition and rating, because they are the best protection for accuracy and safety.
- A circuit you are allowed to work on, with a known or expected voltage.
- Clip leads or fine probes for a tight board layout.
Step-by-step: measure voltage across a resistor
1. Confirm the circuit type
Decide whether the supply is DC or AC. A battery, a regulated DC supply, or a DC rail on a board is DC. Mains wiring and transformer outputs are AC. Setting the wrong function can give a wrong reading or a meter fault.
2. Set the dial
Turn the dial to DC voltage (⎓) or AC voltage (⏦). Fluke suggests starting with the DC voltage setting when unsure, because it handles higher voltages. If you expect a small voltage, use a millivolt range if your meter has one.
3. Set the range
Modern multimeters default to autorange. For a fixed range, press the range button to step through the options. If the reading falls into a lower millivolt range, Fluke advises disconnecting the probes, changing the dial to DC millivolts, and reconnecting.
4. Insert the leads
Plug the black lead into COM and the red lead into the VΩ jack. Do not leave the leads in the A or mA jacks. Fluke warns that probes left in those inputs while measuring voltage create a short in the measurement circuit.
5. Touch the probes across the resistor
Place the black probe on the side of the resistor closest to circuit ground or the negative rail, and the red probe on the other side. Hold the probes steady and make sure the contact is good. Dirt, solder flux, or oil on the contact point can change the reading.
6. Read the display
Wait for the value to settle. If the display shows a negative sign, the red and black probes are reversed for that voltage. Switch the probes to read the magnitude, and note the polarity in your records.
7. Check the reading against your expectation
Compare the reading with the value you expected from the supply and the circuit. A voltage across a resistor near the full supply voltage suggests that the resistor is carrying little current, or that its other side is not connected. A reading near zero suggests either a short across the resistor or no supply reaching that branch.
8. Disconnect in reverse order
Remove the red lead first, then the black lead. Fluke recommends this order for safety. Turn the meter off to save the battery.
Worked example
Suppose a 5 V DC supply feeds a 1 kΩ resistor in series with a 2 kΩ resistor. The resistors divide the voltage in proportion to their values. Across the 1 kΩ resistor you would expect about 1.67 V, and across the 2 kΩ resistor about 3.33 V. If your meter reads about 1.67 V across the 1 kΩ resistor, the divider is working as expected. If it reads close to 5 V across the 1 kΩ resistor, check whether the 2 kΩ part is open. The example uses ideal values. Real resistors have tolerance, so the reading may differ slightly.
Common mistakes
- Setting AC volts on a DC circuit, or the reverse.
- Leaving the leads in the current jacks, which can short the circuit when you switch to voltage.
- Reversing the probes and reading a negative value without understanding the polarity.
- Using the wrong range on a fixed-range meter, which can hide the true value.
- Touching the metal probe tips with bare fingers during a high-voltage measurement.
Safety notes
Fluke’s fuse guidance warns that voltage and current measurements made with a tester that lacks proper fuse protection can cause serious burns and possibly death. Keep the leads in the voltage jacks for voltage tests, use leads rated for the voltage, and never measure voltage through a path that could short the supply. On mains or high-energy circuits, follow your local electrical rules and use a meter rated for that environment.
Product options
A meter with a clear DC and AC voltage selection and a stable display makes resistor voltage checks easier. One option to consider:
For more on choosing a meter for home and workshop use, see our multimeter guide for DIY. For a wider look at test tools, read our voltage tester pen guide.
What we could not verify
The opened Fluke pages describe the general DC voltage procedure and safety notes. They do not give a published input impedance figure for any specific meter, so we did not state one. We also did not verify a specific accuracy or maximum voltage rating for any model. Check the meter’s manual for those values. The AC voltage procedure was not opened in full, so the steps for AC are kept general.
How we chose
This guide is built from three opened Fluke Learn pages. Each step is checked against the wording of those pages, and anything the pages do not state is marked in the What we could not verify section. We did not rank or test meters for this post, so the product link is only one option among many.
Sources
- Fluke, “How to Measure Resistance with a Digital Multimeter”: https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-resistance (opened)
- Fluke, “How to Measure DC Voltage with a Digital Multimeter”: https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-dc-voltage-with-a-digital-multimeter (opened)
- Fluke, “Choosing the correct fuse for your tester”: https://www.fluke.com/en-us/learn/blog/digital-multimeters/choosing-the-correct-fuse-for-your-tester (opened)
Frequently asked questions
Do I need to remove the resistor to measure its voltage?
No. Voltage is measured in parallel, so the resistor can stay in the circuit.
Why is the reading negative?
The probes are reversed relative to the voltage polarity. Swap them, or read the magnitude and note the polarity.
Can I measure voltage across a resistor with the circuit off?
Reading a voltage with the supply off will usually show zero, or a residual value from a charged capacitor. For a live reading, the circuit must be powered and you must follow safe-work practice.
