⚡ Energy Conversion

Convert between energy units for physics, nutrition, engineering, and everyday use. Supports joules (J), kilojoules (kJ), calories (cal), kilocalories (Cal/kcal), watt-hours (Wh), kilowatt-hours (kWh), BTUs, electronvolts (eV), and foot-pounds.

Energy and work conversion calculates the capacity to perform mechanical, thermal, or electrical work. The SI unit is the Joule (J, 1 N·m). 1 kilojoule (kJ) equals 1,000 Joules, 1 dietary Calorie (kcal) equals 4,184 Joules, 1 British Thermal Unit (BTU) equals approx. 1,055.06 Joules, and 1 kilowatt-hour (kWh) equals 3,600,000 Joules.

Metrological Standards & Base Equation

1 calorie = 4.184 joules. 1 kWh = 3,412 BTU = 3.6 × 10⁶ J. 1 eV = 1.602 × 10⁻¹⁹ J.

Energy conversion factors adhere to the International Union of Pure and Applied Physics (IUPAP) and NIST SP 811. Thermochemical calories and International Steam Table (IT) calories are distinguished with exact NIST conversion ratios.

Primary References: NIST SP 811 (2008 Edition) · CODATA Recommended Values · Standards Directory

Supported Energy Units (9 Total)

Energy Unit Definitions and Scaling Factors
Unit Symbol Unit Name System Equivalent in Joule
J Joule Metric Reference Standard (1 J)
kJ Kilojoule Metric 1 kJ = 1000 J
cal Calorie Metric 1 cal = 4.184 J
kcal Kilocalorie Metric 1 kcal = 4184 J
Wh Watt-hour Other 1 Wh = 3600 J
kWh Kilowatt-hour Other 1 kWh = 3600000 J
eV Electronvolt Scientific 1 eV = 1.602000e-19 J
BTU BTU Imperial 1 BTU = 1055.06 J
therm Therm Imperial 1 therm = 105500000 J

Popular Energy Conversions

Joules to Calories

J → cal — physics & nutrition

kWh to BTU

kWh → BTU — HVAC & energy bills

Calories to Joules

Cal → J — food energy conversion

eV to Joules

eV → J — particle physics

BTU to kWh

BTU → kWh — heating & cooling

Common Use Cases

  • Nutrition & diet tracking (Cal↔kJ)
  • Physics calculations (J↔eV)
  • Energy bills (kWh↔BTU)
  • Exercise & fitness (Cal↔J)
  • HVAC engineering (BTU↔kWh)

Frequently Asked Questions

How many joules in a calorie?

One calorie equals 4.184 joules. A food Calorie (kcal) equals 4,184 joules.

How do I convert kWh to BTU?

Multiply kWh by 3,412 to get BTU. For example, 1 kWh × 3,412 = 3,412 BTU.