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A ceramic capacitor’s printed value is not always the value your circuit receives. In high-dielectric-constant multilayer ceramic capacitors (MLCCs), especially X5R and X7R Class II parts, applying a DC voltage can reduce the effective capacitance substantially. The only dependable way to account for that loss is to use the exact manufacturer part number’s DC-bias (voltage-characteristic) curve at the voltage, temperature and measurement conditions your design will actually see.
There is no universal “X7R loses X percent” rule. Two capacitors with the same nominal capacitance and voltage rating can retain very different values because dielectric formulation, ceramic thickness, package, construction, temperature and test conditions differ. A higher voltage rating alone does not tell you how much capacitance remains.
What DC bias changes in a ceramic capacitor
Nominal capacitance is a specified test value
The capacitance printed in a part number, such as 1 µF, is measured under defined conditions. Those conditions include temperature, frequency, AC test amplitude and, for a voltage-characteristic test, the DC voltage applied across the component. The nominal number therefore describes a reference measurement, not every operating point.
When the capacitor is installed in a circuit with a steady voltage across it, the dielectric is already exposed to an electric field before the small AC signal that represents the capacitance measurement is applied. In high-k ceramic dielectrics, the incremental permittivity changes with that field. The result is a lower small-signal capacitance at the biased operating point than the zero-bias nominal value.
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Which ceramic capacitors are affected most
The effect is chiefly associated with Class II and Class III high-dielectric-constant MLCCs. X5R and X7R are common examples. KEMET describes this voltage coefficient of capacitance (VCC) as a phenomenon in which capacitance decreases under an applied DC voltage. Murata likewise warns that high-dielectric capacitors such as X5R and X7R can change from their nominal value when DC voltage is applied.
Class I temperature-compensating ceramics, particularly C0G, are the useful contrast. Their dielectric is selected for stability, so they do not exhibit the same pronounced DC-bias characteristic as high-k Class II parts. C0G parts generally offer less capacitance per unit volume, so they may not meet a high-capacitance or small-footprint requirement, but they are worth checking whenever capacitance stability is critical.
How much capacitance can disappear?
The loss can range from a minor change to most of the nominal value. The following published figures illustrate the possible scale; they are not generic derating rules.
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| Published example | Conditions stated by the source | Reported result | How to use the figure |
|---|---|---|---|
| TDK Electronics, 2025 | Class II X7R, 1 µF, 630 V; approximately 400 V DC bias | Almost 80% of nominal capacitance is lost because of DC bias | Illustrates one specific part and operating point, not every 1 µF or X7R capacitor |
| TDK Electronics, 2025 | The same example after DC-bias and temperature effects are considered | Approximately 0.2 µF at the operating point | Use only as the stated example’s combined operating-point result |
| KEMET Electronics, publication date not stated on its page; accessed 2026 | Class II or III MLCC at rated-voltage conditions | Decrease can reach 90% in some cases | An upper example showing why a generic safety percentage is unsafe |
In the TDK example, 1 µF nominal does not mean 1 µF in the circuit: the operating-point value is about 0.2 µF after both voltage and temperature effects. A different dielectric, case size, rated voltage or construction can produce a very different curve.
Why a single derating percentage cannot be used
Capacitance retention is a property of the complete part, not just the dielectric code. The main variables are:
- Dielectric formulation: X5R, X7R and other high-k formulations have different field dependence. C0G behaves differently.
- Ceramic thickness and layer construction: KEMET identifies dielectric type and thickness as factors in the severity of VCC. The internal layer stack determines the electric field in each dielectric layer.
- Applied DC voltage: Retention usually changes continuously with bias, so 5 V, 12 V, 48 V and a voltage near the rating can correspond to very different capacitance values.
- Temperature: Temperature characteristics combine with DC-bias effects. The TDK example reaches approximately 0.2 µF only after temperature impact is included.
- AC test conditions: Frequency and AC amplitude affect the measured incremental capacitance. A meter reading at one frequency may not match the manufacturer’s curve.
- Package and manufacturer construction: Two parts with the same nominal value and voltage rating can use different layer counts, dimensions and formulations.
- Tolerance: The initial capacitance tolerance sets the starting point before voltage and temperature derating are applied.
Because all of these variables interact, replacing a missing curve with an assumed 10%, 20% or 50% allowance can leave a design either underspecified or unnecessarily large. Use a part-specific characteristic instead.
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How to calculate effective capacitance for your design
Use this procedure during component selection and again when reviewing a design change. It keeps the nominal value, operating bias and environmental conditions separate.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors- Identify the exact component. Record the manufacturer, complete part number, dielectric (for example X7R or X5R), package size, nominal capacitance, tolerance and rated voltage. Do not stop at “1 µF, 25 V X7R”; several parts can share those descriptors.
- Determine the real DC voltage across the capacitor. Use the worst-case steady-state voltage at the component terminals, not merely the nominal rail label. Include output tolerances, startup or shutdown conditions and any series elements that change the division of voltage. For a capacitor on a switching node, determine the voltage across the capacitor during each relevant operating state.
- Obtain the exact part’s DC-bias curve. Look in the manufacturer data sheet or technical documentation for a capacitance-versus-DC-voltage, voltage-characteristic or DC-bias graph. Curves for a similar package or a different rated voltage are not interchangeable evidence.
- Read the retention at the operating voltage. If the graph is normalized, read the fraction of nominal capacitance that remains. If it is plotted directly in microfarads, read the value at your bias. When the operating voltage falls between graph points, interpolate conservatively rather than assuming the nearest favorable point.
- Apply initial tolerance. Start with the tolerance limit relevant to your circuit. A “10%” part can begin below its nominal value before bias is applied, while a tighter tolerance starts closer to nominal. Keep the tolerance and DC-bias factors visible in your calculation.
- Check temperature behavior. Confirm the specified operating-temperature range and the dielectric’s temperature characteristic. If the manufacturer provides combined temperature and DC-bias data, use it. Otherwise evaluate the relevant temperature and voltage effects together and design to the worst credible combination.
- Check the measurement definition. Match the manufacturer’s frequency, AC test voltage and DC-bias conditions when validating a sample. A capacitance reading without those conditions is incomplete.
- Compare the effective value with the circuit requirement. Use the retained capacitance in the calculation for filtering, timing, resonant frequency, energy storage or control-loop stability. If the effective value is too low, select a different part rather than applying an arbitrary multiplier.
A simple way to document the calculation is:
Ceffective = Cnominal × tolerance factor × DC-bias retention × temperature factor
Use this as a bookkeeping model, not as permission to multiply unrelated headline percentages. The manufacturer’s combined characterization takes precedence when available, because temperature and voltage effects may not be independent.
Worked interpretation of a curve
Suppose the exact part is marked 2.2 µF and its manufacturer curve shows 55% retention at the voltage your circuit applies. The curve-based estimate before tolerance and temperature is 1.21 µF, calculated as 2.2 µF × 0.55. If the design requires at least 1.5 µF under that bias, the part does not qualify even though its label says 2.2 µF. You would then evaluate another part, a larger package, a higher-voltage construction or a stable dielectric such as C0G if the required capacitance is available.
Rated voltage is not a capacitance-retention guarantee
The voltage rating primarily states the maximum specified electrical stress under the manufacturer’s conditions. It does not promise that the capacitor retains its nominal capacitance at that voltage. In fact, a high-voltage Class II part can still show a large DC-bias loss near its rating.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchThe TDK 1 µF, 630 V X7R example demonstrates the distinction: at approximately 400 V, the part loses almost 80% of nominal capacitance from DC bias, and the stated operating-point value is approximately 0.2 µF after temperature is included. The rating tells you the allowed voltage class; the voltage-characteristic curve tells you the capacitance delivered there.
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How to measure capacitance under bias
Bench measurements are useful only when their conditions are stated and comparable. For Class II and III devices, KEMET advises considering both applied AC and DC voltages when measuring. Frequency and AC amplitude influence the incremental capacitance that an instrument reports.
- Record the instrument model, test frequency and AC test amplitude.
- Apply the intended DC bias across the capacitor using a safe, current-limited bias network or an instrument designed for biased impedance measurements.
- Allow the component and fixture to reach the intended temperature before recording the value.
- Measure at several bias points so the trend can be compared with the manufacturer curve, rather than relying on one reading.
- Use the same fixture parasitic correction and connection method for each candidate part.
- Compare your result only with manufacturer data taken under matching or clearly understood conditions.
A handheld LCR meter that measures at near-zero bias can therefore report a value close to nominal while the assembled circuit delivers much less capacitance at its operating voltage. That difference is not necessarily an instrument fault; it may simply be a different test condition.
Choosing between candidate MLCCs
Evaluate candidates on the dimensions that determine the capacitance your circuit will actually receive.
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| Selection axis | Question to answer | Why it matters |
|---|---|---|
| Effective capacitance at bias | What value remains at the worst-case DC voltage? | This is the value used by the circuit, not the label alone. |
| Temperature range and behavior | Does the part meet the full operating range, and is combined data available? | Temperature can further reduce or shift capacitance. |
| Package size | Can the required retained capacitance fit the available footprint and height? | Construction and layer geometry affect DC-bias performance. |
| Nominal value and tolerance | What is the initial minimum and maximum before bias? | Bias derating starts from the actual tolerance limits. |
| Rated voltage | Does the part meet electrical stress and transient requirements? | Necessary for reliability, but not a retention specification. |
| Manufacturer characterization | Is a curve available for this exact part number? | Part-specific evidence is safer than a generic dielectric rule. |
| Alternative dielectric | Can a C0G part provide the needed capacitance and footprint? | C0G offers greater stability when its lower capacitance density is acceptable. |
When comparing two parts, rank them by retained capacitance at the operating point first. A part with a larger printed value can deliver less usable capacitance than a smaller nominal part with better DC-bias behavior.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Common design mistakes and their fixes
Using the printed value in every equation
Symptom: A filter’s measured corner frequency is higher than calculated, a timing interval is short, or a converter’s control loop behaves differently from simulation.
Fix: Recalculate with the effective capacitance from the exact part’s DC-bias curve, then include tolerance and temperature.
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Applying one rule to every X7R or X5R capacitor
Symptom: A generic “derate by 20%” policy is used across packages and voltage ratings.
Fix: Replace the rule with a part-number-specific curve review. KEMET’s statement that losses can reach 90% in some cases shows why one percentage cannot cover all Class II and III parts.
Confusing voltage rating with capacitance stability
Symptom: A designer chooses a higher-rated capacitor expecting it automatically to retain its nominal value.
Fix: Verify both requirements independently: rated voltage for electrical stress and the DC-bias characteristic for capacitance retention.
Reading a zero-bias meter value as the in-circuit value
Symptom: Incoming inspection passes, but the circuit has insufficient capacitance under load.
Fix: Measure with the intended DC bias, temperature, frequency and AC amplitude, or use the manufacturer’s characterization under those conditions.
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Ignoring operating transients
Symptom: The design works at the nominal rail but fails during startup, load changes or a high-voltage operating mode.
Fix: Identify the highest actual voltage across the capacitor and evaluate capacitance at each materially different operating state. Also verify that transient voltage remains within the rated-voltage requirement.
Substituting a similar-looking part
Symptom: A second-source component with the same label changes the circuit response.
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When C0G is the better choice
Choose C0G when the circuit depends on a comparatively stable capacitance and the required value, voltage rating and physical size are available. C0G is a Class I temperature-compensating dielectric and does not have the same pronounced high-k DC-bias behavior described for X5R and X7R.
C0G is not an automatic replacement: its capacitance density is lower, so a physically larger component or a smaller capacitance may be necessary. If the required value cannot be obtained in C0G, select a Class II MLCC whose effective capacitance at the real bias meets the requirement and document that curve-based result.
A practical review checklist
- Exact manufacturer part number recorded.
- Dielectric type identified as C0G, X5R, X7R or another specified class.
- Nominal capacitance and tolerance recorded.
- Package size and rated voltage verified.
- Worst-case DC voltage across the component identified.
- Manufacturer DC-bias curve found for the exact part.
- Effective capacitance read at the operating voltage.
- Temperature range and temperature effect included.
- Measurement frequency, AC amplitude and DC bias documented.
- Effective value checked against the circuit’s minimum requirement.
- Any substitute part re-evaluated rather than assumed equivalent.
The essential distinction is simple: the nominal value is a reference specification, while the effective value under your circuit’s DC bias is the value that determines performance. For high-k MLCCs, use the exact manufacturer curve, include temperature and test conditions, and treat voltage rating and capacitance retention as separate design questions.
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