RFrftools.io
Convert

Energy Unit Converter

Convert energy between joules, millijoules, electron-volts, kilowatt-hours, calories, and BTU.

Loading calculator...

Formula

1 kWh = 3.6 MJ, 1 eV = 1.602 × 10⁻¹⁹ J

How It Works

Energy is measured in joules (J), the SI unit equal to one watt-second. Electronics uses a wide range: electron-volts (eV, 1.602 × 10⁻¹⁹ J) for semiconductor physics and photon energy, millijoules (mJ) for ESD pulses and capacitor discharge, joules for mechanical impact and relay coil energy, and kilowatt-hours (kWh) for battery and power system capacity. Calories (1 cal = 4.184 J) and BTU (1 BTU = 1055 J) appear in thermal management contexts.

Worked Example

A 100 μF capacitor charged to 50 V stores E = ½CV² = ½ × 100e-6 × 50² = 0.125 J = 125 mJ = 125,000 μJ. A smartphone battery of 10 Wh = 36,000 J = 36 kJ = 10,000 mWh = 0.01 kWh.

Practical Tips

  • ✓ESD standards specify discharge energy in mJ — the human body model involves ~1 μJ at 2 kV, but the high peak current is what damages ICs.
  • ✓Battery capacity in mAh must be multiplied by voltage to get energy: 2000 mAh at 3.7 V = 7.4 Wh = 26,640 J.
  • ✓Thermal: 1 BTU raises 1 pound of water by 1°F; 1 calorie raises 1 gram of water by 1°C. For electronics thermal design, use joules and watts consistently.

Common Mistakes

  • ✗Confusing energy (joules) with power (watts) — energy = power × time; a 100 W device running for 1 hour consumes 360,000 J = 0.1 kWh.
  • ✗Mixing up eV (electron-volt) with V (volt) — eV is a unit of energy, not voltage. A 1 eV photon has energy 1.602 × 10⁻¹⁹ J.
  • ✗Using kWh and Wh interchangeably — 1 kWh = 1000 Wh = 3,600,000 J. A 10 Wh battery is not 10 kWh.

Frequently Asked Questions

A small calorie (cal) = 4.184 J; it raises 1 gram of water by 1°C. A food Calorie (Cal or kcal) = 1000 cal = 4184 J. Electronics thermal calculations use joules directly.
The energy of electrons in atoms, photons in optics, and bandgaps in semiconductors is naturally on the eV scale. Silicon has a bandgap of 1.12 eV; GaN is 3.4 eV; photon energy of 600 nm light is about 2.07 eV.
Despite voltages of 1–15 kV, ESD pulses contain very little energy (μJ to mJ range). The damage comes from the high peak current (1–10 A) concentrated in a tiny gate oxide, causing dielectric breakdown.
Multiply mAh by 3.6 and by the nominal voltage: Energy (J) = mAh × 3.6 × V. Example: 3000 mAh at 3.7 V = 3000 × 3.6 × 3.7 = 39,960 J ≈ 40 kJ = 11.1 Wh.

Related Calculators

General

Capacitor Energy

Calculate energy stored, charge, and current in capacitors for power supply design

General

Inductor Energy

Calculate energy stored in an inductor, L/R time constant, and current rise time

Power

Battery Life

Estimate battery runtime for IoT and portable devices given average current draw, duty cycle, self-discharge rate, and depth-of-discharge cutoff. Suitable for LiPo, alkaline, NiMH, and coin-cell batteries.

Convert

Frequency ↔ Wavelength

Convert frequency to wavelength in any medium. Calculates full, half, and quarter wavelengths for antenna design, transmission line, and RF system planning.

Convert

dBm ↔ Watts

Convert RF power between dBm, Watts, milliwatts, dBW, dBμV, and RMS volts into 50Ω. Essential for link budgets, amplifier analysis, and RF system design.

Convert

Temperature Converter

Convert temperature between Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur scales. Useful for thermal analysis, datasheet comparison, and engineering calculations.