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Capacitance Calculator

Calculation Type

Charge (Coulombs)

Voltage (V)

Capacitance Formulas

C = Q ÷ V

Capacitance from charge and voltage

E = ½ × C × V²

Energy stored in capacitor

τ = R × C

RC time constant

Parallel Capacitors

C_total = C₁ + C₂ + C₃ + ...

Capacitance adds up. Voltage is same across all.

Series Capacitors

1/C_total = 1/C₁ + 1/C₂ + ...

Total is less than smallest. Charge is same on all.

What Is Capacitance Calculation?

Capacitance measures a capacitor's ability to store electrical charge, measured in farads (F). The fundamental relationship is C = Q ÷ V, where C is capacitance, Q is charge in coulombs, and V is voltage. In practical circuits, capacitors store energy in electric fields and are essential for power supply filtering, signal coupling, motor starting, power factor correction, and energy storage. Common capacitance values range from picofarads (pF) in RF circuits to thousands of microfarads (μF) in power supplies and farads (F) in supercapacitors. This calculator helps determine capacitance from charge and voltage, or calculate related parameters for circuit design.

How to Calculate Capacitance Calculation

1
Select Calculation Mode
Choose what to calculate: capacitance from charge and voltage, charge from capacitance and voltage, or voltage from charge and capacitance.
2
Enter Known Values
Input the two known quantities. Use appropriate units — farads, microfarads (μF), nanofarads (nF), or picofarads (pF) for capacitance; coulombs for charge; volts for voltage.
3
Review the Result
The calculator displays the unknown value. For circuit design, verify the result makes sense for your application — μF for power supplies, nF-pF for RF and timing circuits.
4
Apply to Circuit Design
Use the calculated value to select a standard capacitor. Capacitors come in standard values (E-series) — select the nearest standard value above your calculated requirement.

Why Capacitance Calculation Matters

Power Supply Design

Capacitors smooth rectified AC into stable DC voltage. Calculating proper capacitance ensures adequate filtering, preventing ripple voltage from affecting sensitive electronic circuits and reducing noise.

Motor Starting and Running

AC motors use start capacitors (100-400μF) for high starting torque and run capacitors (5-50μF) for efficiency. Correct capacitance values prevent motor overheating and ensure proper operation.

Power Factor Correction

Capacitor banks improve power factor by supplying reactive power locally. Proper capacitance calculation reduces utility demand charges and improves voltage regulation in industrial facilities.

Timing Circuits

RC timing circuits use capacitors with resistors to create delays and oscillations. The time constant τ = R × C determines timing accuracy for applications from debouncing to PWM generation.

Electrical Safety Tips & Best Practices

Voltage Derating

Always select capacitors rated at least 50% above the maximum circuit voltage. A capacitor in a 12V circuit should be rated 25V or higher. This prevents dielectric breakdown and extends capacitor life.

Electrolytic Capacitors Are Polarized

Aluminum electrolytic capacitors must be connected with correct polarity — positive to positive. Reversed polarity causes gas generation, swelling, and potentially violent failure.

ESR Matters at High Frequencies

Equivalent Series Resistance (ESR) causes power dissipation and reduces filtering effectiveness at high frequencies. Use low-ESR capacitors for switching power supply output filtering.

Parallel Capacitors Add

Capacitors in parallel: C_total = C1 + C2 + C3... Capacitors in series: 1/C_total = 1/C1 + 1/C2 + 1/C3... Use parallel combinations to achieve non-standard capacitance values.

Common Capacitor Values

Value	In Farads	Common Use
1 pF	0.000000000001	RF circuits, tuning
10 pF	0.00000000001	High frequency circuits
100 pF	0.0000000001	Radio frequency
1 nF	0.000000001	Timing, filtering
10 nF	0.00000001	Decoupling, filtering
100 nF	0.0000001	Decoupling, noise suppression
1 µF	0.000001	Audio coupling, timing
10 µF	0.00001	Power supply filtering
100 µF	0.0001	Power supply bulk
1000 µF	0.001	Power supply smoothing
10000 µF	0.01	High-current power supplies

Frequently Asked Questions

What is capacitance?

Capacitance is the ability of a component to store electrical charge. It's measured in farads (F), where 1 farad stores 1 coulomb of charge at 1 volt. Most capacitors are measured in µF (microfarads), nF (nanofarads), or pF (picofarads).

What is the RC time constant?

The time constant (τ = RC) is the time it takes for a capacitor to charge to 63.2% of the supply voltage (or discharge to 36.8%). After 5 time constants, the capacitor is considered fully charged/discharged (99.3%).

When to use series vs parallel?

Use parallel to increase total capacitance or when you need the same voltage across all capacitors. Use series to reduce capacitance or increase voltage rating (each capacitor sees a portion of total voltage).

How much energy does a capacitor store?

Energy increases with the square of voltage: E = ½CV². A 1000µF capacitor at 50V stores 1.25 joules. At 100V, it stores 5 joules (4× more for 2× voltage).

What is a farad?

A farad (F) is the SI unit of capacitance, named after Michael Faraday. One farad stores one coulomb of charge at one volt. Practical capacitors are measured in microfarads (μF = 10⁻⁶ F), nanofarads (nF = 10⁻⁹ F), or picofarads (pF = 10⁻¹² F). Supercapacitors can reach hundreds or thousands of farads.

How do I calculate energy stored in a capacitor?

Energy stored: E = ½ × C × V², where E is energy in joules, C is capacitance in farads, and V is voltage. A 1000μF capacitor charged to 50V stores 1.25 joules. This energy is released when the capacitor discharges and can be dangerous at high voltages.

What is the difference between ceramic and electrolytic capacitors?

Ceramic capacitors are non-polarized, small, cheap, and available from pF to tens of μF. Electrolytic capacitors are polarized, larger, and available from 1μF to thousands of μF. Ceramic is preferred for high-frequency decoupling; electrolytic for bulk energy storage and filtering.

How does temperature affect capacitance?

Temperature stability depends on dielectric material. Ceramic X7R varies ±15% over -55°C to +125°C. C0G/NP0 ceramics are stable within ±30ppm/°C. Electrolytic capacitors lose capacitance at low temperatures and have shorter life at high temperatures (life halves per 10°C above rating).

References & Industry Standards

IEC 60384 - Fixed Capacitors for Use in Electronic Equipment
IEEE 18 - Standard for Shunt Power Capacitors
EIA-198 - Ceramic Dielectric Capacitors Classes I, II, III, and IV
JEDEC Standards for Capacitor Specifications

Last updated: 2026-02-01 | Reviewed by UnitTables Engineering Team

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Capacitance Formulas

C = Q ÷ V

Capacitance from charge and voltage

E = ½ × C × V²

Energy stored in capacitor

τ = R × C

RC time constant

Parallel Capacitors

C_total = C₁ + C₂ + C₃ + ...

Capacitance adds up. Voltage is same across all.

Series Capacitors

1/C_total = 1/C₁ + 1/C₂ + ...

Total is less than smallest. Charge is same on all.

What Is Capacitance Calculation?

How to Calculate Capacitance Calculation

Select Calculation Mode

Choose what to calculate: capacitance from charge and voltage, charge from capacitance and voltage, or voltage from charge and capacitance.

Enter Known Values

Input the two known quantities. Use appropriate units — farads, microfarads (μF), nanofarads (nF), or picofarads (pF) for capacitance; coulombs for charge; volts for voltage.

Review the Result

The calculator displays the unknown value. For circuit design, verify the result makes sense for your application — μF for power supplies, nF-pF for RF and timing circuits.

Apply to Circuit Design

Use the calculated value to select a standard capacitor. Capacitors come in standard values (E-series) — select the nearest standard value above your calculated requirement.

Why Capacitance Calculation Matters

Power Supply Design

Motor Starting and Running

AC motors use start capacitors (100-400μF) for high starting torque and run capacitors (5-50μF) for efficiency. Correct capacitance values prevent motor overheating and ensure proper operation.

Power Factor Correction

Capacitor banks improve power factor by supplying reactive power locally. Proper capacitance calculation reduces utility demand charges and improves voltage regulation in industrial facilities.

Timing Circuits

RC timing circuits use capacitors with resistors to create delays and oscillations. The time constant τ = R × C determines timing accuracy for applications from debouncing to PWM generation.

Electrical Safety Tips & Best Practices

Voltage Derating

Electrolytic Capacitors Are Polarized

Aluminum electrolytic capacitors must be connected with correct polarity — positive to positive. Reversed polarity causes gas generation, swelling, and potentially violent failure.

ESR Matters at High Frequencies

Equivalent Series Resistance (ESR) causes power dissipation and reduces filtering effectiveness at high frequencies. Use low-ESR capacitors for switching power supply output filtering.

Parallel Capacitors Add

Capacitors in parallel: C_total = C1 + C2 + C3... Capacitors in series: 1/C_total = 1/C1 + 1/C2 + 1/C3... Use parallel combinations to achieve non-standard capacitance values.

Common Capacitor Values

Value	In Farads	Common Use
1 pF	0.000000000001	RF circuits, tuning
10 pF	0.00000000001	High frequency circuits
100 pF	0.0000000001	Radio frequency
1 nF	0.000000001	Timing, filtering
10 nF	0.00000001	Decoupling, filtering
100 nF	0.0000001	Decoupling, noise suppression
1 µF	0.000001	Audio coupling, timing
10 µF	0.00001	Power supply filtering
100 µF	0.0001	Power supply bulk
1000 µF	0.001	Power supply smoothing
10000 µF	0.01	High-current power supplies

Frequently Asked Questions

What is capacitance?

What is the RC time constant?

When to use series vs parallel?

How much energy does a capacitor store?

Energy increases with the square of voltage: E = ½CV². A 1000µF capacitor at 50V stores 1.25 joules. At 100V, it stores 5 joules (4× more for 2× voltage).