Energy Converter

Joules, kilowatt-hours, and BTU

Energy is the capacity to do work or transfer heat. Three units dominate everyday technical talk:

• Joule (J) — the SI unit (one newton-metre). Physics textbooks and many engineering datasheets use joules or kilojoules.
• Kilowatt-hour (kWh) — what electricity meters bill. One kilowatt sustained for one hour equals 3.6 million joules.
• British thermal unit (BTU) — still common for heating, cooling, and gas appliance ratings in US customary contexts.

Power (watts) is energy per unit time; this page converts stored or transferred energy, not instantaneous power. For horsepower and kilowatts of power, use the Power converter.

Conversion factors

Values are linked through joules using standard engineering factors:

• 1 kWh = 3,600,000 J
• 1 BTU (International Table) ≈ 1,055.06 J

Edit any field and the others update from that shared joule amount so comparisons stay consistent.

Worked example

Running a 1 kW heater for 2 hours uses 2 kWh, which is 7.2 MJ (7,200,000 J) or roughly 6,824 BTU. A small room air-conditioner rated around 5,000 BTU/h is a power (rate) rating; multiplying by hours of operation would turn that into energy transferred.

Choosing a unit

Use kWh for household electricity and EV charging cost estimates. Use joules or kilojoules when matching SI textbook problems or scientific papers. Use BTU when reading US HVAC capacity plates or older heating charts. Keep dietary kilocalories separate — food energy is handled on the Nutrition page.

Common mistakes

• Treating kW and kWh as interchangeable — kW is power; kWh is energy.
• Mixing BTU (energy) with BTU/h (cooling power).
• Comparing different BTU definitions at extreme precision without stating which table you used.

FAQs

Is heat the same as electricity energy?

They share units, but efficiency losses mean one kWh of electrical input rarely becomes one kWh of useful heat in a real appliance.

Where do joules appear in batteries?

Battery packs are often quoted in Wh or kWh; multiply watt-hours by 3,600 to get joules.

Full guide: Energy units: joules, kWh, and BTU

Related: Power, Nutrition, Temperature.