To measure a potentiometer, you set a multimeter to resistance mode and test across its three terminals: first the two outer pins for total resistance, then the middle pin against each outer pin while turning the shaft. This tells you whether the component matches its rated value and whether the wiper moves smoothly without dead spots. The whole process takes about two minutes.
Identifying the Three Terminals
A potentiometer is an adjustable resistor with three pins. The two outer pins connect to opposite ends of a resistive strip, and the middle pin connects to the wiper, a small contact that slides along that strip when you turn the knob or move the slider. The rated value printed on the component (for example, 10 kΩ or 100 kΩ) is the total resistance between those two outer pins.
When you turn the shaft to the right, resistance between the wiper and the right pin decreases while resistance between the wiper and the left pin increases. The two wiper-to-end readings always add up to roughly the total resistance. Understanding this relationship is the key to every test below.
What You Need
Any digital multimeter with a resistance (Ω) setting will work. If possible, remove the potentiometer from the circuit before testing. Measuring it while it’s still soldered in can give misleading readings because other components in the circuit create parallel resistance paths that pull your numbers lower than the true value. If desoldering isn’t practical, at minimum disconnect power to the circuit first.
Step 1: Measure Total Resistance
Set your multimeter to the resistance range that covers the potentiometer’s rated value. Touch one probe to Terminal 1 (the left outer pin) and the other probe to Terminal 3 (the right outer pin). The reading should be close to the value printed on the component.
“Close” doesn’t mean exact. Manufacturing tolerances for potentiometers are wider than most people expect. Wire-wound types typically fall within ±5% of their rated value. Conductive plastic types, which are very common, can be ±15 to 20% off. So a 10 kΩ conductive plastic pot reading 8.5 kΩ is within spec, not defective. This tolerance applies only to total resistance and doesn’t affect the accuracy of the pot’s proportional output in a circuit.
If the reading is wildly off, shows infinite resistance (open circuit), or reads zero, the resistive element is damaged and the pot needs replacing.
Step 2: Test the Wiper
This is the more important test. It reveals whether the potentiometer adjusts smoothly or has worn out internally.
Place one probe on Terminal 1 (left outer pin) and the other on Terminal 2 (the middle/wiper pin). Slowly rotate the shaft from one end to the other. Watch the multimeter display: the resistance should climb or fall steadily with no sudden jumps. Then move your probe from Terminal 1 to Terminal 3 (right outer pin), keep the other on the wiper, and repeat the rotation. You should see the resistance move in the opposite direction this time.
For linear slider pots and membrane-style pots (like SoftPots or ThinPots), the process is the same. Instead of rotating a shaft, you press or slide along the strip while watching the meter. Resistance should change smoothly with finger position.
What a Healthy Pot Looks Like
On a good potentiometer, the resistance changes continuously with no jumps, dropouts, or flickering digits on the display. At one extreme of rotation, the wiper-to-near-end resistance should drop close to zero. At the other extreme, it should read close to the full rated value. The two wiper readings (wiper-to-left plus wiper-to-right) should roughly equal the total resistance you measured in Step 1 at any point in the rotation.
What Bad Readings Tell You
Potentiometers fail in predictable ways, and the multimeter makes each one visible.
- Sudden jumps or spikes: The resistance leaps erratically as you turn the shaft. This means the wiper has worn through the resistive element in spots, creating poor contact. These “dead spots” cause crackling in audio equipment and erratic behavior in control circuits.
- Open circuit at certain positions: The meter briefly flashes to infinite resistance during rotation. The wiper is losing contact with the resistive track entirely at that point.
- No change at all: The reading stays fixed no matter how you turn the shaft. Either the wiper is broken off internally or it’s jammed.
- Infinite resistance between outer terminals: The resistive element itself is cracked or burned open. The pot is completely failed.
Any of these patterns means the potentiometer should be replaced. There’s no practical way to repair a worn resistive element.
Linear vs. Audio Taper: What to Expect
How the resistance changes during your wiper test depends on the potentiometer’s taper type, and this catches people off guard if they don’t know what they’re looking at.
A linear taper pot (usually marked with a “B” on the body) changes resistance at a constant rate. At the halfway point of rotation, you’ll read roughly half the total resistance. At one-quarter turn, roughly one-quarter. The relationship between position and resistance is proportional, and the response is linear between about 5% and 95% of the rotation range.
An audio or logarithmic taper pot (marked “A”) behaves very differently on a meter. The resistance changes slowly through most of the rotation, then rises or falls steeply near one end. At the halfway point, you won’t read half the total resistance. It might be 10 or 15% of the total value instead. This exponential curve is designed to match how human ears perceive volume: it sounds like a smooth, even increase to the listener even though the electrical change is lopsided. If you’re testing an audio taper pot and the resistance seems to “do nothing” for most of the turn before changing rapidly, that’s normal behavior, not a fault.
Checking a Pot Used as a Variable Resistor
Sometimes a potentiometer is wired using only two of its three terminals, functioning as a simple variable resistor (also called a rheostat). In this configuration, you only need to test between the two connected terminals. Place your probes on those pins and rotate the shaft. The resistance should sweep from near zero up to whatever portion of the total resistance the circuit uses.
One thing to watch with this configuration is power handling. A potentiometer’s power rating (often 0.25W or 0.5W for small panel-mount types) applies to the full resistance element. When you dial a variable resistor down to a low setting, the same voltage across a much smaller resistance means significantly more power dissipation. A 1 kΩ pot rated at half a watt, for example, would be limited to about 22 volts across the full element but could overheat at much lower voltages if the wiper is set near one end. If a pot you’re testing shows burn marks or discoloration on the body, excessive current at a low resistance setting is a likely cause.
Quick Reference for Common Readings
- Total resistance within ±20% of rated value: Normal for most types.
- Wiper sweeps smoothly from near zero to near full value: Healthy pot.
- Linear taper reads ~50% at midpoint: Confirms linear type, working correctly.
- Audio taper reads ~10–15% at midpoint: Confirms audio type, working correctly.
- Any flicker, jump, or dropout during rotation: Worn or dirty. Try contact cleaner first on older pots, but replacement is often the better fix.