Introduction
A capacitor is a device that stores electrical energy in an electric field. It is made of two metal plates separated by a gap or an insulating material called a dielectric. Capacitors are found in almost every electronic circuit, from phone chargers to car engines. This capacitor calculator helps you quickly find key values like capacitance, charge, voltage, and energy stored. Just enter the values you know, and the calculator does the math for you. Whether you are a student learning about circuits or someone working on an electronics project, this tool makes solving capacitor problems fast and simple.
How to Use Our Capacitor Calculator
This calculator has four tools that help you decode capacitor codes, find charge or voltage, check tolerance ranges, and calculate series or parallel capacitance. Enter your known values and the calculator does the rest.
Capacitor Code (Code Decoder tab): Type in a 3-digit capacitor code, such as 104 or 473. The first two digits are the main number, and the third digit tells how many zeros to add. The calculator converts the code into picofarads (pF), nanofarads (nF), and microfarads (µF).
Capacitance (Q = C × V tab): Enter the capacitance of your capacitor and pick a unit from the dropdown menu. Options include pF, nF, µF, mF, and F. Fill in this field along with one other field, and the calculator will solve for the missing value.
Voltage (Q = C × V tab): Enter the voltage across the capacitor and choose a unit such as mV, V, or kV. When you provide voltage along with either capacitance or charge, the calculator finds the unknown third value using the formula Q = C × V. If you need to explore the relationship between voltage, current, and resistance in other parts of your circuit, try our Ohm's Law Calculator.
Charge (Q = C × V tab): Enter the electric charge stored on the capacitor and select a unit like pC, nC, µC, mC, or C. If you leave this field empty but fill in both capacitance and voltage, the calculator will compute the charge for you.
Nominal Capacitance (Tolerance tab): Enter the rated capacitance printed on your capacitor and choose its unit. This is the starting value the calculator uses to figure out the minimum and maximum possible capacitance based on the tolerance you set.
Tolerance Input Mode (Tolerance tab): Pick either "Letter Code" or "Percentage." Letter Code lets you choose a standard tolerance letter like J (±5%) or K (±10%). Percentage mode lets you type in any custom tolerance value. The calculator then shows the lowest and highest capacitance your component could actually have, along with a visual bar. You can use the Percentage Calculator to quickly verify tolerance percentages if needed.
Connection Type (Series & Parallel tab): Choose either "Series" or "Parallel" to tell the calculator how your capacitors are wired. Series capacitors share the same charge, while parallel capacitors share the same voltage. The formula used changes based on your choice.
Capacitor List (Series & Parallel tab): Enter the value and unit for each capacitor in the list. You start with three capacitors, and you can add more by clicking the "+ Add Capacitor" button or remove one by clicking the red "✕" button. The calculator shows the total equivalent capacitance and a bar chart comparing each capacitor.
Target Equivalent Capacitance (Series & Parallel tab): If you leave exactly one capacitor in the list blank, this field appears. Enter the equivalent capacitance you want to achieve, and the calculator will work backward to find the missing capacitor value needed to reach that target.
What Is a Capacitor?
A capacitor is an electronic component that stores electrical energy in an electric field. It is made of two metal plates separated by an insulating material called a dielectric. When voltage is applied across the plates, one plate builds up positive charge and the other builds up negative charge. This stored charge can be released later to power a circuit. Capacitors are found in almost every electronic device, from smartphones and computers to power supplies and electric motors.
How Capacitance Is Measured
Capacitance is the ability of a capacitor to store charge. It is measured in farads (F). One farad is a very large amount of capacitance, so most real-world capacitors are measured in smaller units:
- Microfarads (µF) — one millionth of a farad (10−6 F)
- Nanofarads (nF) — one billionth of a farad (10−9 F)
- Picofarads (pF) — one trillionth of a farad (10−12 F)
Working with very large or very small numbers like these is easier when you use scientific notation.
Reading a 3-Digit Capacitor Code
Small capacitors often have a 3-digit code printed on them instead of a full value. The first two digits are the significant figures, and the third digit tells you how many zeros to add after them. The result is always in picofarads (pF). For example, the code 104 means 10 followed by four zeros, which equals 100,000 pF (or 100 nF, or 0.1 µF). The code 473 means 47 followed by three zeros, giving 47,000 pF.
The Charge Formula: Q = C × V
The fundamental equation for capacitors is Q = C × V, where Q is the electric charge stored (in coulombs), C is the capacitance (in farads), and V is the voltage across the capacitor (in volts). If you know any two of these values, you can always solve for the third. For instance, a 100 µF capacitor charged to 12 V stores 1,200 µC of charge. This relationship is analogous to Ohm's law for resistors — if you need to work with resistance and current, our Ohm's Law Calculator can help.
Capacitor Tolerance
No capacitor is manufactured to an exact value. Tolerance tells you how much the actual capacitance can differ from the labeled (nominal) value. Tolerance is shown as either a percentage or a letter code. Common letter codes include J (±5%), K (±10%), and M (±20%). For very small capacitors, tolerance may be given as an absolute value in picofarads, such as B (±0.1 pF). The asymmetric code Z (+80% / −20%) means the capacitor could be much larger than its label but only slightly smaller. Knowing the tolerance range is important when designing circuits that need precise timing or filtering. To understand how small deviations affect your measurements, the Percent Error Calculator is a useful companion tool.
Series and Parallel Capacitors
When capacitors are connected together in a circuit, their combined (equivalent) capacitance depends on how they are wired:
- Parallel: The total capacitance is the simple sum of all individual capacitances. Ctotal = C1 + C2 + C3 + … Connecting capacitors in parallel always gives you more total capacitance.
- Series: The total capacitance is found using reciprocals. 1/Ctotal = 1/C1 + 1/C2 + 1/C3 + … Connecting capacitors in series always gives you less total capacitance than the smallest individual capacitor. Series connections are used when you need a higher voltage rating or a specific small capacitance value.
For example, three capacitors of 100 µF, 220 µF, and 470 µF connected in parallel give 790 µF total. Connected in series, the same three give roughly 55.7 µF.
Why Capacitor Calculations Matter
Choosing the right capacitor value is critical in circuit design. Capacitors smooth out voltage in power supplies, set timing intervals in oscillator circuits, block DC current while passing AC signals, and store energy for camera flashes or emergency backup systems. The energy stored in a capacitor is closely related to concepts like potential energy and kinetic energy in mechanical systems. Using this calculator, you can quickly decode capacitor markings, find charge or voltage from known values, check the real-world range a capacitor's tolerance allows, and figure out equivalent capacitance for series or parallel networks. For broader circuit analysis involving voltage, current, and power, pair this tool with our Ohm's Law Calculator and Force Calculator to cover the full range of physics problems you may encounter.