A resistor's resistance value tells you whether it still works
A multimeter measures electrical properties, and the resistance setting (marked with the Greek letter omega, Ω) tells you whether a resistor is functioning. A working resistor will show a reading close to its rated value — printed on the component itself or marked with colored bands. A resistor that reads zero, infinity, or wildly off its rated value is likely damaged and should be replaced.
The test takes about 30 seconds and requires only a multimeter and the resistor itself. You do not need to power anything on, and you can test a resistor while it is still soldered to a circuit board, though removing it first gives you a cleaner reading.
Key Takeaways
- Set your multimeter to the resistance (ohms) setting, choosing a range that matches or exceeds the resistor's rated value.
- Touch one probe to each end of the resistor and wait for the reading to stabilize — a working resistor shows a value close to its rated resistance.
- A reading of zero ohms means the resistor is shorted; a reading of infinity (or "OL" on the display) means it is open and broken.
- Remove the resistor from the circuit board if the reading seems wrong, because other components nearby can affect the measurement.
- Resistor color bands or printed labels tell you the expected value — compare the meter reading to this number to confirm the resistor is good.
Locate the resistor's rated value before testing
Every resistor has a labeled resistance value, measured in ohms. On larger resistors, this value is printed directly on the body. On smaller components (common in modern electronics), colored bands wrap around the resistor — each band represents a digit or multiplier.
If you are unsure how to read color bands, a resistor color code chart is available online; you can also photograph the resistor and use an image search tool. The rated value tells you what the meter should read if the resistor is working correctly. For example, a resistor marked "470Ω" should read close to 470 ohms.
Write down or remember the expected value before you start testing. This makes it easy to spot when a reading is wrong.
Set the multimeter to the correct resistance range
Turn the multimeter's dial to the resistance setting, marked with the Ω symbol. Most multimeters have multiple resistance ranges: ×1, ×10, ×100, ×1k (1,000), ×10k, and sometimes ×100k or higher. The range you choose affects how the meter displays the reading.
Select a range that matches or exceeds the resistor's rated value. For a 470-ohm resistor, the ×100 or ×1k range works well. For a 10,000-ohm (10k) resistor, use ×1k or ×10k. If you are unsure, start with a higher range — you can always switch down if the reading is too small to read clearly.
Some modern multimeters have an auto-ranging feature that selects the range for you. If your meter has this, simply turn the dial to the Ω symbol without a number, and the meter will adjust automatically.
Touch the probes to each end of the resistor
Hold the two probe tips against the two ends of the resistor. It does not matter which probe touches which end — resistance is the same in both directions. Press firmly so the probe makes good contact with the resistor's lead or body.
Watch the display. The reading will jump and then settle within a second or two. Once it stops changing, you have your measurement. A working resistor will show a value close to its rated resistance — within about 5 to 10 percent is normal for most resistors.
If the resistor is still soldered to a circuit board, you can test it in place, but the reading may be affected by other components connected nearby. If the result seems wrong, desolder the resistor carefully and test it again in isolation.
Interpret the meter reading to determine if the resistor is good
Compare the meter reading to the resistor's rated value. A reading within 5 to 10 percent of the rated value means the resistor is working. For example, a 1,000-ohm resistor that reads 950 to 1,050 ohms is fine.
A reading of zero ohms means the resistor is shorted — its internal element has failed and is conducting electricity freely. This resistor must be replaced.
A reading of infinity (displayed as "OL" or "∞" on most meters) means the resistor is open — its internal element is broken and no longer conducts. This resistor must also be replaced.
A reading that is significantly higher or lower than expected (more than 10 to 15 percent off) suggests the resistor is degraded or damaged. In circuits where precision matters, replace it. In circuits where the exact value is less critical, you can often leave it in place if it is still within a reasonable range.
Remove the resistor if the reading seems wrong
If the meter shows a reading that does not match the rated value, the resistor itself may be fine — other components on the circuit board can interfere with the measurement. Capacitors, diodes, and other parts connected in parallel with the resistor will change what the meter reads.
To get a true reading, desolder one end of the resistor from the board using a soldering iron or desoldering pump. Leave it connected at one end, or remove it completely. Test again. If the reading is now close to the rated value, the resistor is good and the earlier reading was affected by neighboring components. If the reading is still wrong, the resistor is damaged.
Once you have confirmed the resistor's status, you can resolder it if it is good, or replace it if it is bad.
Frequently Asked Questions
What if the meter shows a reading that is slightly off from the rated value?
Resistors have a tolerance rating, usually 5 or 10 percent, which means the actual value can vary from the printed value by that amount. A 1,000-ohm resistor with 5 percent tolerance can legitimately read anywhere from 950 to 1,050 ohms. Check the resistor's datasheet or color bands to find its tolerance, then compare the meter reading to that range.
Can I test a resistor while it is soldered to the board?
Yes, but the reading may be inaccurate because other components nearby can affect the measurement. If the reading seems wrong, desolder one end of the resistor and test again. This isolates the resistor and gives you a true reading of its resistance.
What does "OL" mean on the multimeter display?
"OL" stands for "overload" or "open limit" and indicates that the resistance is too high for the meter to measure — effectively infinite. This means the resistor is broken and no longer conducts electricity. Replace it.
Do I need to power off the circuit before testing a resistor?
Yes. Always disconnect power from the circuit before using a multimeter to measure resistance. Testing a resistor in a powered circuit can damage the meter or give you a false reading. If the resistor is soldered to the board, power down the device completely before you start.
What if the meter reads zero ohms?
A zero-ohm reading means the resistor is shorted — its internal element has failed and is conducting electricity with no resistance. This resistor cannot do its job and must be replaced. A shorted resistor can also cause other components in the circuit to overheat or fail.