Capacitor Design Calculator

What is a Capacitor Design Calculator?

The Capacitor Design Calculator is an engineering tool that helps you calculate capacitance, charge, stored energy, and physical dimensions for capacitors. A capacitor stores electrical energy by holding opposite charges on two conductive plates separated by an insulator (dielectric).

This calculator covers five related equations: basic capacitance (C = Q/V), stored energy (U = ½CV²), parallel plate capacitance (C = εA/d), and cylindrical (coaxial) capacitance (C = 2πεL / ln(b/a)). Each equation can be used to understand different aspects of capacitor behavior in electronic circuits.

The Capacitor Formulas

Basic Capacitance

C = Q / V

Where:

• C = Capacitance (farads)
• Q = Electric charge (coulombs)
• V = Voltage across the capacitor (volts)

Stored Energy

U = ½ × C × V²

Where:

• U = Stored energy (joules)
• C = Capacitance (farads)
• V = Voltage (volts)

Parallel Plate Capacitor

C = ε × A / d

Where:

• C = Capacitance (farads)
• ε = Dielectric permittivity (F/m)
• A = Plate area (m²)
• d = Separation distance between plates (m)

Cylindrical (Coaxial) Capacitor

C = 2πεL / ln(b/a)

Where:

• C = Capacitance (farads)
• ε = Dielectric permittivity (F/m)
• L = Length of conductors (m)
• b = Outer conductor radius (m)
• a = Inner conductor radius (m)

How to Use This Calculator

Select an "Equation Type" from the dropdown menu. You can choose between Basic Capacitance, Stored Energy, Parallel Plate, or Cylindrical capacitor calculations.

• Basic Capacitance — Enter capacitance and voltage to calculate stored charge.
• Stored Energy — Enter capacitance and voltage to calculate energy stored in the capacitor.
• Parallel Plate — Enter permittivity, plate area, and gap distance to calculate capacitance.
• Cylindrical — Enter permittivity, length, outer radius, and inner radius to calculate capacitance per unit length.

Applications

• Power Supply Design — Size filter capacitors and calculate energy storage for smooth DC output.
• Camera Flash Circuits — Calculate the energy storage needed for flash discharge at specific voltage.
• Coaxial Cable Design — Determine capacitance per unit length of coaxial transmission lines.
• MEMS Sensors — Design parallel plate capacitive sensors for pressure and acceleration measurement.
• Energy Storage Systems — Size capacitor banks for pulsed power and energy storage applications.

Worked Example

Scenario: A parallel plate capacitor has plates with area 0.01 m² separated by 1 mm in a vacuum (ε₀ = 8.85 × 10&supmin;¹² F/m). What is the capacitance?

1. Permittivity ε = 8.85 × 10&supmin;¹² F/m
2. Plate area A = 0.01 m²
3. Gap distance d = 0.001 m
4. Capacitance C = (8.85 × 10&supmin;¹² × 0.01) / 0.001 = 8.85 × 10&supmin;¹¹ F (88.5 pF)