Conversion tool
Energy Converter
Convert between SI, thermal, electrical and mechanical energy units. Bridges physics, engineering and nutrition — all factors NIST-referenced.
Formula & conversion factors
1 kWh = 3,600,000 J (exact, 1 kW × 3,600 s)
1 kcal = 4,186.8 J (International Table calorie, exact)
1 BTU = 1,055.056 J (International Table BTU, NIST SP811)
1 eV = 1.602176634 × 10⁻¹⁹ J (exact, 2019 SI redefinition)
1 ft·lbf = 1.35582 J (NIST SP811)
Note: "calorie" in nutrition labelling (food Calorie) is actually a kilocalorie (kcal). This converter lists both separately.
1 kcal = 4,186.8 J (International Table calorie, exact)
1 BTU = 1,055.056 J (International Table BTU, NIST SP811)
1 eV = 1.602176634 × 10⁻¹⁹ J (exact, 2019 SI redefinition)
1 ft·lbf = 1.35582 J (NIST SP811)
Note: "calorie" in nutrition labelling (food Calorie) is actually a kilocalorie (kcal). This converter lists both separately.
1Worked example: 1 kWh in BTU. 3,600,000 J ÷ 1,055.056 = 3,412.14 BTU (this is the standard conversion used in HVAC load calculations).
Reference standard: Base unit: joule (J), the SI derived unit of energy (1 J = 1 kg·m²/s²).
Conversion factors per NIST SP811 and the 2019 SI redefinition (for eV).
Common questions
What is the difference between a calorie and a Calorie?
A lowercase "calorie" (cal) is the energy to raise 1 g of water by 1 °C (4.1868 J). An uppercase "Calorie" (Cal) used in food labelling equals 1,000 cal = 1 kcal. This converter lists both as "cal" and "kcal" to avoid confusion.
How many BTU are in a kWh?
Approximately 3,412 BTU. This ratio is fundamental to HVAC engineering — it connects electrical energy (kWh) to thermal energy (BTU) for sizing heating and cooling equipment.