Energy Converter — kWh to Joules, eV to J, BTU to kJ

Energy measures how much work or heat is stored or transferred. Electricity bills use kilowatt-hours, food labels use calories, HVAC specs quote BTU, and physics uses joules and electronvolts. This converter switches between those units from one input — pick From and To, enter a value, and read the result instantly.

Supported units include joules (J), kilojoules (kJ), megajoules (MJ), watt-hours (Wh), kilowatt-hours (kWh), megawatt-hours (MWh), BTU, calories (cal/kcal), and electronvolts (eV). All math runs locally in your browser; nothing is uploaded.

Energy and power are related but not interchangeable. Power (watts, kilowatts) is the rate at which energy flows. Energy (joules, kWh) is power multiplied by time.

• 1 kilowatt = 1,000 watts — a power scaling, not an energy unit.
• 1 watt sustained for one hour = 1 watt-hour (Wh) of energy.
• Energy (kWh) = power (kW) × time (hours).

A 2 kW heater running for 3 hours consumes 6 kWh — enter 6 kWh here to convert to joules or BTU. Horsepower (about 745.7 W) is also a power unit; convert the resulting energy once you know kWh or joules.

Utility bills bill electrical energy in kilowatt-hours (kWh). In India and some regions, one kWh is colloquially called one "unit" of electricity on domestic meters — 100 units means 100 kWh.

1 kWh = 1,000 Wh = 3,600,000 J = 3.6 MJ

One megawatt-hour (MWh) equals 1,000 kWh. Battery capacity is often quoted in amp-hours (Ah); converting Ah to kWh requires voltage (Wh = Ah × V). Once you have watt-hours or kWh, use this converter directly.

The SI unit for energy is the joule (J). Common conversion factors:

1 kWh = 3.6 × 10⁶ J · 1 BTU ≈ 1,055 J · 1 kcal = 4,184 J · 1 cal ≈ 4.184 J

One BTU is about 1.055 kJ or 0.000293 kWh. HVAC ratings sometimes quote BTU per hour (BTU/h), which is a power rate — for energy, convert BTU to kWh with the factor above. Natural gas volumes are sometimes quoted in gigajoules (GJ): 1 GJ ≈ 947,817 BTU.

Food labels use kilocalories (kcal), often written "Calories." 2,000 kcal per day is about 8,368 kJ — not all of that becomes usable mechanical work in the body.

In atomic and particle physics, energy is often quoted in electronvolts (eV). The conversion to joules is exact under the 2019 SI definition:

1 eV = 1.602176634 × 10⁻¹⁹ J  ·  1 J ≈ 6.242 × 10¹⁸ eV

Example: 1 MeV = 10⁶ eV ≈ 1.602 × 10⁻¹³ J. Electronvolts are an energy unit (charge × voltage), not a voltage conversion. One joule equals 10⁷ ergs in the older CGS system.

• 1 kWh = 3,600,000 J = 3.6 MJ ≈ 3,412 BTU
• 1 BTU ≈ 1.055 kJ ≈ 0.293 Wh
• 1 kcal ≈ 4.184 kJ ≈ 3.97 BTU
• 9 kWh ≈ 32.4 MJ (typical daily home use in many countries)
• 1 eV ≈ 1.602 × 10⁻¹⁹ J (single atomic-scale quantum)

A 2 kW device running for one hour consumes 2 kWh — convert that 2 kWh here to joules or BTU for comparison with other scales.

This tool converts energy units — not thermodynamic processes. Heat-to-electricity efficiency, mechanical-to-electrical conversion in generators, and fuel chemistry (coal to CO₂, gas volume to energy) need domain-specific models beyond unit arithmetic.

Converting joules to kilograms uses Einstein's E = mc² — not a linear unit factor. Power converters handle watts and horsepower. Once you have an energy value in BTU, kWh, or joules, this page handles the unit switch.