Calculator inputs
Custom material library
Saved materials remain in this browser. Values should come from reliable test data.
Material comparison
Selecting the same field shows how permittivity changes energy density. Breakdown values are approximate and vary by conditions. Always consult manufacturer data before design decisions.
| Material | Relative permittivity | Energy density at current field | Approximate breakdown |
|---|---|---|---|
| Vacuum | 1 | 4.427094 J/m³ | Not specified |
| Air | 1.0006 | 4.429750 J/m³ | 3 MV/m |
| Paper | 3.5 | 15.494829 J/m³ | 16 MV/m |
| Glass | 5.5 | 24.349016 J/m³ | 12 MV/m |
| Mica | 6 | 26.562563 J/m³ | 120 MV/m |
| Ceramic (general) | 10 | 44.270939 J/m³ | 20 MV/m |
| PTFE / Teflon | 2.1 | 9.296897 J/m³ | 60 MV/m |
| Polyethylene | 2.3 | 10.182316 J/m³ | 25 MV/m |
| Polystyrene | 2.6 | 11.510444 J/m³ | 24 MV/m |
| Transformer oil | 2.2 | 9.739607 J/m³ | 12 MV/m |
| Water (low frequency) | 80 | 354.167513 J/m³ | 65 MV/m |
Sensitivity charts
The first chart varies electric field while keeping permittivity fixed. The second chart varies permittivity at one field. Both charts use the standard uniform-field equation.
Calculation history
| Time | Material | Field | εᵣ | Energy density |
|---|
Formula used
Using displacement: u = ½(E · D) = D²/(2ε)
Parallel plates: E = V/d
Total energy: U = uVolume
Capacitor energy: U = ½CV²
Energy density grows with the square of electric field. Doubling field strength makes the density four times larger. Permittivity creates a directly proportional change in linear media.
How to use this calculator
- Select the equation matching your available electrical data.
- Choose a dielectric preset or enter custom permittivity.
- Enter field, displacement, voltage, geometry, or capacitance values.
- Select units, waveform settings, and desired numerical precision.
- Add volume when total stored energy is required.
- Review warnings, breakdown margin, conversions, and calculation steps.
- Export results using copy, CSV, PDF, or print.
Example data
| Example | Inputs | Method | Expected energy density |
|---|---|---|---|
| Air field | E = 1 MV/m, εᵣ = 1.0006 | ½εE² | About 4.43 J/m³ |
| PTFE dielectric | E = 5 MV/m, εᵣ = 2.1 | ½εE² | About 232.42 J/m³ |
| Parallel plates | V = 2 kV, d = 1 mm, εᵣ = 4 | E = V/d, then ½εE² | About 70.83 J/m³ |
Assumptions and limitations
The main equations assume a linear and isotropic dielectric. They also assume a locally uniform electric field. Fringing, saturation, hysteresis, and losses need advanced field analysis.
Material permittivity changes with frequency and temperature. Moisture, defects, aging, and pressure can change breakdown strength. Use laboratory or manufacturer values for safety-critical engineering work.
The breakdown comparison is an educational screening estimate. It does not replace insulation coordination or certified testing. Maintain suitable safety factors for real electrical equipment designs.
Frequently asked questions
What is electric field energy density?
It measures stored electrical energy within each unit volume. Its standard SI unit is joules per cubic meter. Larger fields generally store much more energy in materials.
Why is the electric field squared?
Field energy follows a quadratic relationship in linear dielectrics. A doubled field therefore creates four times the density. This makes high-field systems especially sensitive to input errors.
What permittivity should I enter?
Use relative permittivity from the material data sheet. Frequency and temperature should match your intended operating conditions. Measured values are best for critical engineering calculations.
Can this calculate total stored energy?
Yes, enter the region volume for field-based modes. Capacitor mode can calculate energy directly from capacitance. Geometry also allows energy density to be calculated afterward.
What is the difference between peak and RMS?
Peak is the maximum sinusoidal field magnitude. RMS is peak divided by the square root of two. Average energy uses the selected field basis appropriately.
Does dielectric material always increase stored energy?
At fixed electric field, higher permittivity increases energy density. At fixed free charge, the relationship can behave differently. The physical constraint must match the selected calculator mode.
How accurate are breakdown strength presets?
They are approximate reference values for initial screening. Thickness, defects, humidity, waveform, and test method matter. Always replace presets with verified material specifications.
Can I use this for nonuniform fields?
The calculator reports a local or uniform-field approximation. Nonuniform systems require integrating density throughout the full volume. Finite-element software is often used for complex geometries.
Are magnetic energy effects included?
No, this page calculates only electric field energy. Electromagnetic systems can also contain magnetic energy density. Add both contributions when total field energy is required.