What Is ESR in a Capacitor? Typical ESR Values Table

How to Measure ESR

ESR cannot be accurately measured with a standard multimeter's resistance mode. A multimeter measures DC resistance, but ESR is an AC parameter measured at a specific frequency (typically 100kHz for aluminum electrolytic capacitors). You need one of these tools:

• Dedicated ESR meter — Inexpensive handheld meters (like the Peak Atlas ESR70 or Blue ESR meter) are purpose-built for in-circuit ESR measurement. They apply a small AC signal at 100kHz and display ESR directly in ohms or milliohms.
• LCR meter — Professional LCR bridges (like the BK Precision 880 or Keysight U1733C) measure ESR as part of a full impedance characterization. Set the test frequency to 100kHz for electrolytics or 1MHz for ceramics.
• Impedance analyzer — For engineering-level analysis, an impedance analyzer can sweep ESR across a frequency range, revealing the capacitor's behavior from DC through RF. This is how manufacturers generate datasheet impedance curves.

For a complete walkthrough of capacitor testing methods, see our how to test a capacitor guide.

What Causes High ESR?

ESR increases over a capacitor's lifetime due to several degradation mechanisms:

• Electrolyte evaporation — The #1 cause of ESR rise in aluminum electrolytic capacitors. The liquid electrolyte slowly escapes through the rubber seal, increasing internal resistance. This process accelerates exponentially with temperature — capacitor life roughly halves for every 10°C above the rated temperature. Read more in our why capacitors fail guide.
• Oxide layer degradation — In tantalum and aluminum electrolytic capacitors, the thin oxide dielectric can develop defects that increase leakage and ESR.
• Internal connection corrosion — Moisture ingress or chemical reaction between internal materials can corrode tab connections, increasing resistance at the electrode-to-lead interface.
• Mechanical stress — Thermal cycling, vibration, and physical shock can crack solder joints between the capacitor's internal foils and external leads.

ESR Effects by Application

High ESR manifests differently depending on where the capacitor is used:

• Switch-mode power supplies — High ESR in output filter capacitors causes excessive output ripple voltage (V_ripple = I_ripple × ESR). This can trigger instability, cause audible noise, damage sensitive ICs, or prevent the power supply from starting. This is the most common capacitor failure mode in consumer electronics, industrial equipment, and UPS systems.
• Motor start/run circuits — Rising ESR in motor capacitors reduces the phase shift needed for starting torque, causing hard starts, overheating, or failure to start entirely. See our motor capacitor troubleshooting guide.
• Audio amplifiers — High ESR in power supply filter capacitors reduces dynamic headroom, causing bass sag, increased hum, and reduced output power. In audio applications, even modest ESR increases are audible.
• DC link in power electronics — Elevated ESR in power converter DC link capacitors causes internal heating, which further accelerates degradation in a thermal runaway feedback loop.

ESR by Capacitor Technology

Different capacitor dielectrics have fundamentally different ESR characteristics:

• Aluminum electrolytic — Highest ESR of common types. ESR decreases with increasing capacitance and decreasing voltage rating. Low-ESR series (designed for SMPS use) have 2-10× lower ESR than general-purpose types of the same value.
• Polymer aluminum — Conductive polymer electrolyte provides 5-10× lower ESR than liquid electrolyte types. No dry-out failure mode. Preferred for CPU/GPU VRM output filtering.
• Film capacitors — Very low ESR across all frequencies. ESR is dominated by metallization resistance and lead/terminal connections. Self-healing property means ESR may increase slightly after clearing events but the capacitor continues functioning.
• Ceramic MLCC — Extremely low ESR at high frequencies, making them ideal for RF bypass and decoupling. However, ESR is highly frequency-dependent and varies with temperature and DC bias.
• Tantalum — ESR falls between electrolytic and polymer types. MnO₂ cathode tantalums have moderate ESR; polymer cathode tantalums approach polymer aluminum performance.

When to Replace Based on ESR

As a practical rule for maintenance and repair:

• If measured ESR exceeds the datasheet maximum by more than 50%, replace the capacitor
• If ESR is 2× or more the value of a known-good capacitor of the same type and value, replace it
• If the capacitor shows any physical symptoms (bulging, leaking, discoloration) in addition to elevated ESR, replace immediately regardless of readings
• For preventive maintenance in critical systems (UPS, medical, industrial), replace electrolytic capacitors at 5-7 year intervals even if ESR appears normal — degradation can accelerate rapidly once it begins

Need replacement capacitors? Request a quote or browse our electrolytic capacitor inventory. For obsolete or hard-to-find parts, our sourcing team can locate replacements from our global network.