An ohmmeter can show you whether a capacitor is completely dead, but it cannot tell you if the capacitor works correctly under real conditions

When you connect an ohmmeter to a capacitor, you are measuring resistance across its plates. A working capacitor will show a specific pattern: the needle or digital display will jump toward zero resistance at first, then climb back toward infinity as the capacitor charges. A capacitor that is shorted (failed with its plates touching internally) will stay at zero. A capacitor that is open (broken connection inside) will stay at infinity. Neither of these patterns means the capacitor is good — it means the capacitor is broken in a way an ohmmeter can detect.

The reason this test is limited is that an ohmmeter measures only resistance, not capacitance. A capacitor can fail in ways that do not show up as a resistance problem. It can lose its ability to hold a charge, develop a leak that drains it slowly, or fail only when voltage is applied. An ohmmeter will not catch any of these failures. If you need to know whether a capacitor actually works, you need a multimeter set to capacitance mode or a dedicated capacitance meter.

Key Takeaways

  • A working capacitor will show the needle or display jump toward zero, then slowly climb back toward infinity as you measure it with an ohmmeter.
  • A shorted capacitor stays at zero resistance; an open capacitor stays at infinity — both are broken, but in different ways.
  • An ohmmeter test only catches complete failures, not capacitors that have lost capacitance or leak charge over time.
  • For a real test of whether a capacitor works, use a multimeter in capacitance mode or a dedicated capacitance meter instead.

How to set up the ohmmeter test

Disconnect the capacitor completely from the circuit before you test it. If power is still flowing through the circuit, the ohmmeter reading will be wrong and you risk damaging the meter. If the capacitor is large or has been in use, it may still hold a charge even after power is off — discharge it by touching a screwdriver or wire across both leads to ground the stored energy safely.

Set your multimeter to the ohms setting, usually marked with the Greek letter omega (Ω). If your meter has multiple ohms ranges (×1, ×10, ×100, ×1000), start with the ×1 or ×10 range for small capacitors. For larger capacitors, you may need a higher range. Touch the red probe to one lead and the black probe to the other lead. The order does not matter for this test.

What the needle or display does during the test

At the moment you touch the probes to the capacitor leads, the display will jump sharply toward zero ohms (or the needle will swing toward the left side of an analog meter). This happens because the capacitor is charging from the small voltage the ohmmeter supplies. As the capacitor fills with charge, its resistance appears to increase, and the needle or display will climb back toward the right side of the scale (toward infinity or the highest ohms reading).

On a digital multimeter, you will see the number start low and climb higher. On an analog meter with a needle, you will watch the needle swing left, then slowly creep back to the right. This back-and-forth motion is the sign of a capacitor that is not shorted or open. The speed of the climb depends on the capacitor's size — a large capacitor charges slowly and takes longer to climb, while a small one climbs quickly.

Reading a shorted capacitor

A shorted capacitor will show zero ohms and stay there. The needle will not move back toward infinity, and a digital display will hold at or very close to zero. This means the internal plates of the capacitor are touching, creating a direct path for current. A shorted capacitor is completely failed and must be replaced.

Shorted capacitors are dangerous in circuits because they can draw large amounts of current and generate heat. If you find one, remove it from the circuit and replace it with a new capacitor of the same voltage and capacitance rating. Do not try to repair or reuse a shorted capacitor.

Reading an open capacitor

An open capacitor will show infinite resistance and stay there. The needle will not move at all on an analog meter, or a digital display will show "OL" (overload) or a very high number like 9999. This means there is a break inside the capacitor — the connection between the plates or the lead is severed, so no current can flow at all.

An open capacitor is also completely failed. In a circuit, an open capacitor will block any signal or current that tries to pass through it. Replace it with a new capacitor of the same voltage and capacitance rating. An open capacitor is safer than a shorted one because it does not draw current, but it still stops the circuit from working correctly.

Why this test has limits

An ohmmeter test catches only the most obvious failures — a short or an open. It does not measure the actual capacitance (the ability to store charge), so it cannot tell you if a capacitor has lost half its capacitance and is now too weak for the circuit. It also cannot detect a leaky capacitor, which slowly drains its charge even when no current is flowing. Both of these failures will cause a circuit to behave strangely, but an ohmmeter will show the capacitor as "good" because the resistance is still climbing back toward infinity.

Electrolytic capacitors (the cylindrical ones with polarity markings) are especially prone to leaking and losing capacitance as they age. An ohmmeter will not catch this degradation. If you suspect a capacitor is weak rather than completely dead, or if you need to verify that a capacitor meets its rated capacitance, use a multimeter in capacitance mode or a dedicated capacitance meter.

When to use capacitance mode instead

If your multimeter has a capacitance mode (usually marked with a symbol like —| |— or the letter F for farads), use that instead of the ohmmeter test. Capacitance mode directly measures how much charge the capacitor can hold and will show you the actual capacitance value. Compare this reading to the value printed on the capacitor's body. If the reading is significantly lower than the rating, the capacitor has failed and needs replacement.

Capacitance mode is faster and more reliable than the ohmmeter test. It will catch weak or leaky capacitors that an ohmmeter test would miss. If your meter does not have capacitance mode, a dedicated capacitance meter costs between $20 and $60 and is worth the investment if you work with electronics regularly.

Frequently Asked Questions

Can I test a capacitor while it is still connected to the circuit?

No. The rest of the circuit will interfere with the reading and may give you a false result. Always disconnect the capacitor completely before testing. If the capacitor is soldered to a board, desolder at least one lead so the capacitor is isolated.

Why does the needle move back and forth on an analog meter?

The ohmmeter supplies a small voltage to measure resistance. The capacitor charges from this voltage, so its resistance appears to drop at first. As it fills with charge, it stops accepting current, and the resistance climbs back. This charging action is what you are seeing when the needle moves.

What if the needle does not move at all?

If the needle stays at infinity and does not jump toward zero at all, the capacitor is open — there is a break inside it. If the needle stays at zero and does not climb back, the capacitor is shorted. Both are complete failures and the capacitor must be replaced.

Can an ohmmeter test tell me if a capacitor is the right size for my circuit?

No. An ohmmeter only tells you if the capacitor is shorted or open. To verify the capacitance value, you need a multimeter in capacitance mode or a dedicated capacitance meter. Check the reading against the value printed on the capacitor's body.

Is it safe to touch the capacitor leads while testing?

Yes, the voltage from an ohmmeter is very small and safe to touch. However, if the capacitor was recently in a powered circuit, it may still hold a charge. Discharge it first by touching a wire across both leads to ground, then test it safely.