How to Calculate Voltage Across a Capacitor (Made Simple for Beginners)

✨ Master the basics of charge, time, and stored energy in just a few steps!

If you’re working with electronics or learning about circuits, chances are you’ve come across a capacitor — the small but mighty component that stores electrical energy. But how do you figure out how much voltage is across it?

Let’s walk through it in a simple way.

🙋 What Is a Capacitor?

A capacitor is a device that stores energy in an electric field. It does this by holding positive charge on one plate and negative charge on the other. The more charge it stores, the more voltage you’ll see across its terminals.

🧮 The Basic Formula

The voltage across a capacitor depends on two things:

  • The amount of charge (Q) on it
  • Its capacitance (C) — measured in farads (F)

Here’s the formula:

V = Q ÷ C

Where:

  • V = voltage across the capacitor (volts)
  • Q = charge in coulombs (C)
  • C = capacitance in farads (F)

So if you know how much charge is stored, and the capacitor’s value, you can calculate the voltage!

🔌 Simple Charge Calculation

You have a capacitance of 220 µF (microfarads), and a charge of 0.022 coulombs.

Step 1: Convert 220 µF to farads:
220 µF = 220 × 10⁻⁶ F = 0.00022 F

Step 2: Use the formula:

V = Q ÷ C = 0.022 ÷ 0.00022 = 100 volts

So the capacitor has 100V across its plates.

⏱️ Charging a Capacitor Over Time

In real circuits, capacitors charge over time, especially in RC circuits (Resistor-Capacitor circuits). The formula for voltage over time is:

V(t) = Vmax × (1 - e^(-t / RC))

Where:

  • V(t) = voltage at time t
  • Vmax = supply voltage
  • t = time (in seconds)
  • R = resistance (ohms)
  • C = capacitance (farads)
  • e ≈ 2.718 (Euler’s constant)

The tool below shows how a capacitor charges exponentially — fast at first, then slowing down as it fills.

⚡ Capacitor Charging Graph

🌐 Real-World Use

You might need to calculate capacitor voltage if you’re:

  • Designing a power supply or timer circuit
  • Working with audio filters
  • Using energy storage systems
  • Analyzing voltage smoothing in AC-to-DC conversion

📌 Quick Tips

  • Use V = Q ÷ C for instant voltage
  • For RC circuits, use the exponential charging formula
  • Capacitance is often given in µF or nF, so convert to farads first!
  • Voltage ratings are important — don’t exceed what the capacitor is rated for