Conversion method
A food Calorie is a kilocalorie: 1 kcal = 4,184 J, while 1 small calorie = 4.184 J. kWh measures energy, not power. This registry uses the international-table BTU convention.
kJ = x × 4.184
10 kcal = 41.84 kJ.
| kcal | kJ |
|---|---|
| 1 | 4.184 |
| 5 | 20.92 |
| 10 | 41.84 |
| 25 | 104.6 |
| 50 | 209.2 |
| 100 | 418.4 |
Unit definitions and sources
Calories are thermochemical; BTU uses the International Table definition. US therms use the separate US definition. Electronvolt multiples (keV, MeV, GeV, TeV) use the exact SI electronvolt, 1.602176634 × 10⁻¹⁹ J.
36 of the 47 definitions below were checked against the cited sources on 2026-09-20 (AI-assisted check).
| Unit and system | Use | Definition | Relationship |
|---|---|---|---|
| Joule (J); si | Common units | Joule measures energy. j = (value in J) × 1. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kilojoule (kJ); si | Common units | Kilojoule measures energy. j = (value in kJ) × 1000. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Megajoule (MJ); si | Common units | Megajoule measures energy. j = (value in MJ) × 1000000. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Calorie (thermochemical) (cal); other | Common units | Calorie (thermochemical) measures energy. j = (value in cal) × 4.184. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kilocalorie (food calorie) (kcal); other | Common units | Kilocalorie (food calorie) measures energy. j = (value in kcal) × 4184. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Watt-hour (Wh); si | Common units | Watt-hour measures energy. j = (value in Wh) × 3600. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kilowatt-hour (kWh); si | Common units | Kilowatt-hour measures energy. j = (value in kWh) × 3600000. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| British thermal unit (IT) (BTU); us | Common units | British thermal unit (IT) measures energy. j = (value in BTU) × 1055.05585262. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Therm (US) (thm); us | Specialist units | Therm (US) measures energy. j = (value in thm) × 105480400. Common use: Energy use and heat. | Approximate / conventional |
| Foot-pound (ft·lbf); us | Specialist units | Foot-pound measures energy. j = (value in ft·lbf) × 1.3558179483314003. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Electronvolt (eV); si | Specialist units | Electronvolt measures energy. j = (value in eV) × 1.602176634e-19. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Erg (erg); other | Specialist units | Erg: multiply by 1e-07 to obtain the category base unit. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Calorie (International Table) (cal IT); other | Specialist units | Calorie (International Table): multiply by 4.1868 to obtain the category base unit. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| BTU (thermochemical) (BTU th); other | Specialist units | BTU (thermochemical): multiply by 1054.3502644888888 to obtain the category base unit. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Megaelectronvolt (MeV); other | Specialist units | Megaelectronvolt: multiply by 1.602176634e-13 to obtain the category base unit. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kiloelectronvolt (keV); other | Specialist units | Kiloelectronvolt: 1 keV = 10^3 eV = 1.602176634e-16 J, from the exact electronvolt 1.602176634 × 10^-19 J. Common use: Particle, nuclear and X-ray photon energies. | Exact definition; numerical display may be rounded |
| Gigaelectronvolt (GeV); other | Specialist units | Gigaelectronvolt: 1 GeV = 10^9 eV = 1.602176634e-10 J, from the exact electronvolt 1.602176634 × 10^-19 J. Common use: Particle, nuclear and X-ray photon energies. | Exact definition; numerical display may be rounded |
| Teraelectronvolt (TeV); other | Specialist units | Teraelectronvolt: 1 TeV = 10^12 eV = 1.602176634e-7 J, from the exact electronvolt 1.602176634 × 10^-19 J. Common use: Particle, nuclear and X-ray photon energies. | Exact definition; numerical display may be rounded |
| Exajoule (EJ); si | Specialist units | exajoule: E denotes 10^18; the unit gives 1000000000000000000 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Petajoule (PJ); si | Specialist units | petajoule: P denotes 10^15; the unit gives 1000000000000000 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Terajoule (TJ); si | Specialist units | terajoule: T denotes 10^12; the unit gives 1000000000000 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Gigajoule (GJ); si | Specialist units | gigajoule: G denotes 10^9; the unit gives 1000000000 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Hectojoule (hJ); si | Specialist units | hectojoule: h denotes 10^2; the unit gives 100 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Decajoule (daJ); si | Specialist units | decajoule: da denotes 10^1; the unit gives 10 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Decijoule (dJ); si | Specialist units | decijoule: d denotes 10^-1; the unit gives 0.1 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Centijoule (cJ); si | Specialist units | centijoule: c denotes 10^-2; the unit gives 0.01 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Millijoule (mJ); si | Specialist units | millijoule: m denotes 10^-3; the unit gives 0.001 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Microjoule (µJ); si | Specialist units | microjoule: µ denotes 10^-6; the unit gives 0.000001 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Nanojoule (nJ); si | Specialist units | nanojoule: n denotes 10^-9; the unit gives 1e-9 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Picojoule (pJ); si | Specialist units | picojoule: p denotes 10^-12; the unit gives 1e-12 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Femtojoule (fJ); si | Specialist units | femtojoule: f denotes 10^-15; the unit gives 1e-15 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Attojoule (aJ); si | Specialist units | attojoule: a denotes 10^-18; the unit gives 1e-18 j. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Btu (IT) (BTU IT); other | Specialist units | Btu (IT) = 1055.05585262 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Gigawatt-hour (GW·h); other | Specialist units | gigawatt-hour = 3600000000000.0 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Megawatt-hour (MW·h); other | Specialist units | megawatt-hour = 3600000000.0 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Newton meter (N·m); other | Specialist units | newton meter = 1.0 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kilocalorie (IT) (kcal IT); other | Specialist units | kilocalorie (IT) = 4186.8 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kilocalorie (th) (kcal th); other | Specialist units | kilocalorie (th) = 4184.0 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Calorie (th) (cal th); other | Specialist units | calorie (th) = 4.184 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Dyne centimeter (dyn·cm); other | Specialist units | dyne centimeter = 1e-07 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Gram-force meter (gf·m); other | Specialist units | gram-force meter = 0.00980665 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Gram-force centimeter (gf·cm); other | Specialist units | gram-force centimeter = 9.80665e-05 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kilogram-force centimeter (kgf·cm); other | Specialist units | kilogram-force centimeter = 0.0980665 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Kilogram-force meter (kgf·m); other | Specialist units | kilogram-force meter = 9.80665 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Pound-force foot (lbf·ft); other | Specialist units | pound-force foot = 1.3558179483314003 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Pound-force inch (lbf·in); other | Specialist units | pound-force inch = 0.11298482902761668 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
| Ounce-force inch (ozf·in); other | Specialist units | ounce-force inch = 0.007061551814226043 j, derived from the component SI/customary definitions. Common use: Energy use and heat. | Exact definition; numerical display may be rounded |
Sources: BIPM: International System of Units; NIST: SP 811 Appendix B.8: conversion factors; NIST: 2022 CODATA recommended constants; BIPM: SI prefixes
Precision of energy conversions
All 47 energy units convert through Joule (J). 46 have an exact defined relationship to the base unit and 1 is conventional or measured values. Results and the tables on this page come from the same engine, so a table value can be checked against the converter directly.
Standard display shows up to six decimal places, switching to scientific notation for very large or small values. Calculation uses JavaScript binary floating point independently of display rounding, so extra digits are not a claim about measurement accuracy. Each unit lists its own source; a citation records where the definition comes from, not an independent review. See Conversion methodology for the review and correction process.