Capacitor Size Calculator
You can run this capacitor size calculator to find the capacitance required to handle a given voltage and a specific start-up energy.
"What size capacitor do I need?"
If you ask yourself this question a lot, you might like to find out how to calculate capacitor size, and what "capacitor size" even means at all. We also provide you with all necessary formulae you would need to do it by hand. Keep reading!
What is capacitance?
Capacitance is a fundamental property of a capacitor that measures its ability to store electrical charge when a voltage is applied across it. This property is a key ingredient in the capacitor size formula, because it quantifies the relationship between the stored charge and the resulting voltage.
Formally, capacitance is defined as the ratio of the magnitude of the electric charge stored on one plate of a capacitor to the potential difference or voltage across the capacitor:
- — capacitance in Farads () which you can check, e.g., in the capacitor size chart in the next section;
- — charge stored on one plate of the capacitor in Coulombs (); and
- — voltage across the capacitor in Volts ().
Don't confuse these quantities' symbols with their units' symbols!
In simpler terms, capacitance represents how much charge a capacitor can store per unit of voltage. A higher capacitance value indicates that a larger amount of charge can be stored for a given voltage.
The capacitance of a capacitor depends on various factors, such as:
- Physical design;
- Surface area of the plates;
- Distance between the plates; and
- Dielectric material used between the plates.
The dielectric material is crucial in determining the capacitance since it affects the capacitor's ability to store charge.
Capacitance is typically measured in units such as Farads (F), but smaller units such as microfarads (μF), nanofarads (nF), and picofarads (pF) are commonly used in practical applications.
Capacitance has significant implications for circuit design and functionality since capacitors are used in various electronic systems for energy storage, filtering, voltage regulation, timing circuits, and coupling or decoupling signals.
🙋 You can learn more about capacitance checking out our capacitance calculator.
Capacitor size chart
The capacitance and the voltage rating can be used to find the so-called capacitor code. The voltage rating is defined as the maximum voltage that a capacitor can withstand. This coding system helps identify and select the appropriate capacitor for electronic circuitry. The capacitor code also allows you to find the capacitance of a capacitor. You can see some examples in following capacitor size chart:
You can check our capacitor code calculator to learn how to determine the capacitor code and access a complete list of capacitance conversion.
How to calculate the capacitor size?
The capacitor size calculator is based on the concept of the start-up energy stored in a capacitor. Such energy is computed using the equation:
- — Start-up energy;
- — Capacitor size or capacitance (see the next equation to learn how to calculate capacitor size); and
- — Voltage of a capacitor.
From this previous equation, you can see that the capacitor size formula is
The standard units for measuring , , and are farads, joules, and volts, respectively. To run the capacitor size calculator, you must provide the values for the start-up energy and the voltage of your electric motor.
What size of capacitor do I need?
Let's suppose that your electric motor has a voltage of , and you consider a start-up energy of . The capacitor size formula shows that the capacitor size required is .
How can we store energy in a capacitor?
We can store energy in a capacitor by accumulating and storing electric charge on its plates. When a voltage is applied across the capacitor, it creates an electric field between the plates. This electric field causes electrons to accumulate on one plate and creates a deficit of electrons on the other plate.
This process may change if we consider circuits where several capacitors are combined. Connecting several capacitors in series or in parallel will change the total capacitance of the circuit. From the capacitor size formula, we observe that by changing the capacitance, the stored energy also changes.
The stored energy is released back into the circuit when the capacitor is discharged. The capacitor releases its stored charge, and the energy is transformed into other forms, such as electrical work or heat, depending on the circuit configuration and the application.
You can apply the equations presented here to find the capacitor size of an electric motor, and they are also the basic concept behind the functioning of a heart defibrillator. Therefore, capacitors can literally save your life in an emergency — hope you paid attention!