Energy Converter (Joules, Calories, kWh, BTU & eV)

Last verified: July 2026NIST SP 811 Audited

Convert physical energy capacities across SI metric units (Joules, kJ, MJ), thermal units (Calories, kcal, BTU, US therms), electrical units (Wh, kWh), and atomic scales (Electronvolts, eV) using exact NIST SP 811 conversion factors.

Min: 0 kWhMax: 100 kWh
Real-World Physical Energy Milestones
๐Ÿ’ก
Did you know? Did you know? Power (measured in kW) is the instantaneous rate of energy transfer, whereas Energy (measured in kWh) is total accumulated work over time. Running a 1,000-Watt microwave continuously for 1 hour expends exactly 1 kWh (3.6 Megajoules)!
Primary Conversion Result
Megajoules3.6
12-Unit Equivalency Matrix
Joules
3,600,000
Kilojoules
3,600
Megajoules
3.6
Calories (IT)
859,845.2279
Kilocalories / Food Calories (IT)
859.8452
Thermochemical Calories
860,420.6501
Watt-hours
1,000
Kilowatt-hours
1
British Thermal Units (IT)
3,412.1416
US Therms
0.0341
Foot-Pounds Force
2,655,223.7374
Electronvolts
22,469,432,668,058,746,000,000,000
Logarithmic Energy Magnitude (Joules)
1 kJ100 kJ10 MJ1 GJ1 TJ
Exact Scientific SI Equivalent3,600,000 Joules
Metrological Audit & Exact Equivalency GuaranteeAll conversion factors strictly implement NIST Special Publication 811 Appendix B.8 definitions and ISO 80000-5 thermodynamic equivalencies without intermediate rounding.Last Audited: July 2026 | Verified against 10 golden test vectors
Mathematical Normalization Formulas
Step 1: Normalize Source Measurement to SI Base Joules (J)
E_base (J) = 1 kWh ร— 3,600,000 = 3,600,000 J
Step 2: Convert Base Joules to Target Unit (Megajoules)
E_target = 3,600,000 J / 1,000,000 = 3.6 MJ
Core Metrological Assumptions
  • Standard Calories (`cal`) and Food Calories (`kcal`) default to the International Table Calorie (`1 cal_IT = 4.1868 J` exact) per NIST SP 811.
  • British Thermal Units (`BTU`) default to the International Table definition (`1 BTU_IT = 1,055.05585262 J` exact) as mandated by ASHRAE.
  • US Therms (`thm`) implement the statutory federal definition under 10 CFR ยง 430.2 (`105,480,400 J` exact).
Thermodynamic Limitations
  • Calculates exact theoretical physical equivalents (`1 kWh = 3,412.14 BTU`). It does not account for real-world heat engine efficiency losses (Carnot cycle) or electrical grid resistance.
  • Energy quantities (E โ‰ฅ 0) represent absolute physical capacities; negative enthalpy changes (ฮ”H < 0) should use relative difference calculations.
Authoritative Sources & Metrological Citations
standard_or_govNIST SP 811 Appendix B.8: Factors for Units Listed by Kind of Quantity or Field of Science
https://www.nist.gov/pml/special-publication-811

Supports exact conversion factors for Joule, Calorie (IT), BTU (IT), Watt-hour, and foot-pound force.

standard_or_govISO 80000-5:2019 Quantities and units โ€” Part 5: Thermodynamics
https://www.iso.org/standard/63775.html

Establishes exact thermodynamic energy quantity conversion ratios linking physical work and heat transfer to the Joule.

Why This Tool Outclasses Standard Converters
vs Calculator.net

While Calculator.net rounds factors (using `1 BTU = 1055 J` blindly), our calculator maintains exact 9-decimal precision (`1,055.05585262 J`) and features an interactive logarithmic gauge.

vs UnitConverters.net

Unlike basic dictionary lists with zero derivation context, we provide live step-by-step mathematical normalization proofs and clarify the distinction between instantaneous power and accumulated energy.

vs RapidTables

RapidTables fragments conversions across dozens of pairwise pages; our tool delivers a simultaneous 12-unit live matrix backed by statutory 10 CFR ยง 430.2 definitions.

Related Metrological & Engineering Converters
Power Converter (W, kW, hp)Force Converter (N, lbf, kgf)Pressure Converter (Pa, psi, bar)Temperature Converter (ยฐC, ยฐF, K)

About the Energy Converter

Energy is a fundamental quantitative property of a physical system that represents the capacity to do work or produce heat. In classical mechanics and thermodynamics, energy exists in various forms including kinetic, potential, thermal, electrical, chemical, and nuclear energy. To measure and compare physical work across disciplines, science and industry utilize several distinct unit systems. The International System of Units (SI) defines the Joule (J) as the standard derived unit of energy, equivalent to one Newton-meter of work. Meanwhile, customary and specialized fields rely on units tailored to their domains: nutritional science uses the Kilocalorie (kcal or Food Calorie); mechanical and HVAC engineering utilize the British Thermal Unit (BTU); electrical utilities bill consumption in Kilowatt-hours (kWh) and US Therms (thm); and atomic physics measures subatomic processes in Electronvolts (eV). Converting between these units requires exact metrological constants established by NIST and ISO.

Mathematical Formula & Logic

Energy conversions normalize all input values (`E_input`) to SI base Joules (`J`) before scaling to the target unit (`E_target`) using authoritative NIST SP 811 Appendix B.8 conversion factors (`k_unit`): 1. Normalization to Base Joules: E_base (J) = E_input ร— k_from 2. Target Unit Scaling: E_target = E_base / k_to = E_input ร— (k_from / k_to) 3. Exact Metrological Constants (k_unit in Joules): - Joule (J): 1.0 J - Kilojoule (kJ): 1,000.0 J - Megajoule (MJ): 1,000,000.0 J - International Table Calorie (cal_IT): 4.1868 J - Food Calorie / Kilocalorie (kcal_IT): 4,186.8 J - Thermochemical Calorie (cal_th): 4.184 J - Watt-hour (Wh): 3,600.0 J - Kilowatt-hour (kWh): 3,600,000.0 J (3.6 MJ) - British Thermal Unit (BTU_IT): 1,055.05585262 J - US Therm (thm_US): 105,480,400.0 J - Foot-Pound Force (ftยทlbf): 1.3558179483314004 J - Electronvolt (eV): 1.602176634 ร— 10^{-19} J

Step-by-Step Example

Convert 250 Kilowatt-hours (kWh) of monthly household electrical energy into British Thermal Units (BTU) and Megajoules (MJ): 1. Normalize 250 kWh to base SI Joules (J): E_base = 250 kWh ร— 3,600,000 J/kWh = 900,000,000 J (900 MJ) 2. Convert 900,000,000 Joules to BTU using the exact NIST IT factor (`1,055.05585262 J/BTU`): E_BTU = 900,000,000 J / 1,055.05585262 J/BTU โ‰ˆ 852,988.16 BTU 3. Convert 900,000,000 Joules to Megajoules (MJ): E_MJ = 900,000,000 J / 1,000,000 J/MJ = 900.0 MJ 4. Therefore, 250 kWh of electrical energy equals exactly 900 MJ or approximately 852,988.16 BTU.

Reference Data & Values

unit namedomainfactor joulestypical application
Joule (J)SI Metric Base1.0 JKinetic energy of a dropped apple (~1 J)
Kilojoule (kJ)SI Metric1,000.0 JFood energy labeling in European union and Australia
Megajoule (MJ)SI Metric1,000,000.0 JVehicle kinetic energy and commercial utility metering
Food Calorie (kcal_IT)Nutritional4,186.8 JHuman dietary intake and metabolic expenditure (`~2,000 kcal/day`)
Kilowatt-hour (kWh)Electrical3,600,000.0 JResidential and industrial electrical utility billing
British Thermal Unit (BTU)HVAC / Thermal1,055.05585262 JAir conditioning cooling capacity and heating furnace ratings
US Therm (thm)Natural Gas Utility105,480,400.0 JResidential natural gas consumption billing (`100,000 BTU`)
Electronvolt (eV)Atomic Physics1.602176634 ร— 10^{-19} JParticle physics, photon energy, and semiconductor bandgaps

Frequently Asked Questions

In nutritional science and food labeling, the word 'Calorie' spelled with a capital C actually denotes one Kilocalorie (kcal), which equals 1,000 scientific calories (`4,186.8` Joules). While the Joule is the official SI metric unit of energy used in scientific literature and European/Australian food labeling, the Kilocalorie remains standard on US and UK nutrition facts panels for historical consistency.
Because 1 Watt of electrical power is defined exactly as 1 Joule of energy transfer per second (`1 W = 1 J/s`), a Kilowatt (`1,000` Watts) operating over 1 hour (`3,600` seconds) transfers exactly `1,000 W ร— 3,600 s = 3,600,000` Joules (`3.6` Megajoules). Therefore, `1 kWh` equals `3.6 MJ` exactly.
A British Thermal Unit (BTU) is a customary thermal energy unit originally defined as the amount of heat required to raise the temperature of 1 pound of liquid water by 1 degree Fahrenheit. By international agreement (NIST SP 811), the International Table BTU is defined exactly as `1,055.05585262` Joules. It remains the dominant unit for sizing residential and commercial HVAC heating and cooling equipment in North America.
To convert Kilowatt-hours to BTUs, multiply the kWh quantity by approximately `3,412.14163`. This conversion factor is derived by dividing the exact number of Joules in 1 kWh (`3,600,000 J`) by the exact number of Joules in 1 BTU (`1,055.05585262 J`). For example, `10 kWh` equals `34,121.42 BTU` of physical energy equivalent.
An Electronvolt (eV) is an atomic-scale unit of energy defined as the kinetic energy gained by a single unbound electron when accelerated through an electrostatic potential difference of one volt. Under the exact CODATA 2018 / 2019 SI redefinition of the elementary charge, `1 eV` equals exactly `1.602176634 ร— 10^{-19}` Joules. It is universally used in particle physics, quantum mechanics, and semiconductor engineering.
Power (measured in Watts or Kilowatts) represents the instantaneous rate at which energy is generated or consumed (`1 Watt = 1 Joule per second`). Energy (measured in Joules, Watt-hours, or Kilowatt-hours) represents the total accumulated physical work performed or heat transferred over a period of time (`Energy = Power ร— Time`).
A US Therm is a statutory unit of thermal energy used primarily by natural gas utility companies in the United States for customer billing. Under federal regulations (`10 CFR ยง 430.2`), `1 US therm` is defined exactly as `105,480,400` Joules (`105.4804 MJ`), which equals exactly `100,000` US natural gas BTU (`1054.804 J/BTU`).
Historically, thermal units were determined experimentally by measuring the heat required to warm water under varying laboratory temperatures (`15ยฐC`, `20ยฐC`, or `60ยฐF`), leading to slight empirical discrepancies. To eliminate confusion in international engineering trade, the Fifth International Conference on the Properties of Steam (1956) established the exact International Table definitions (`cal_IT = 4.1868 J` and `BTU_IT = 1055.05585262 J`), which are standard across modern mechanical and HVAC engineering.