Energy Converter
Convert between joules, calories, kWh, BTU and more.
Kilojoule (kJ)
418.4
from 100 Kilocalorie (kcal)
Joule (J)
418,400
Calorie (cal)
100,000
Kilocalorie (kcal)
100
Watt-hour (Wh)
116.222222
Kilowatt-hour (kWh)
0.116222
AI Breakdown & Smart Takeaway
Plain-English insight on your numbers
Get a personalized explanation of what these results mean — and how to improve them.
How the Energy Converter works
The GKCalculators Energy Converter instantly converts between joules, calories, kilocalories, kilowatt-hours, BTU, electron volts, and more — making it indispensable for students, engineers, nutritionists, and anyone working across physics, thermodynamics, or energy billing.
At its core, every energy unit is simply a different-sized 'container' measuring the same physical quantity — the capacity to do work or transfer heat. The joule (J) is the SI base unit, defined as the energy transferred when a force of one newton acts over one meter. Every other unit in this converter has a fixed, exact (or very precisely measured) relationship to the joule, so converting between any two units is a matter of multiplying or dividing by the correct factor. The converter chains these factors automatically, meaning you never have to do a two-step manual conversion from BTU to joule to calorie yourself.
A critical distinction that trips up many users is the difference between a small calorie (cal) and a kilocalorie (kcal). One small calorie is the energy needed to raise 1 gram of water by 1 °C (≈ 4.184 J), while one kilocalorie equals 1,000 small calories (≈ 4,184 J). Food labels in the United States and most of Europe list 'Calories' (capital C) which are actually kilocalories — so a chocolate bar listing 250 Calories actually contains 250,000 small calories or roughly 1,046,000 joules. Always confirm which calorie definition a source is using before converting, as mistaking kcal for cal introduces a 1,000× error.
The kilowatt-hour (kWh) is the unit electricity providers use on bills, representing the energy consumed by a 1,000-watt appliance running for one hour (3,600,000 J or 3.6 MJ). The BTU (British Thermal Unit) is the imperial counterpart widely used in HVAC, natural gas billing, and industrial heating in the United States; one BTU ≈ 1,055.06 J. When sizing air conditioners or furnaces, engineers routinely convert between BTU and kWh to reconcile equipment specs with utility costs. Using the wrong unit in these contexts can lead to undersized equipment or significant billing miscalculations.
One common mistake is ignoring thermochemical vs. international table calorie definitions — they differ by a fraction of a percent (4.184 J vs. 4.1868 J per cal), which is negligible for everyday use but matters in precision chemistry or calorimetry. Similarly, electron volts (eV) are used at the atomic scale (1 eV ≈ 1.602 × 10⁻¹⁹ J), so converting eV to joules produces extremely small numbers; always check your exponent. The safest workflow is to identify your source unit precisely, enter the value into the converter, and read the destination unit — letting the converter handle the chain of factors rather than doing mental arithmetic with rounded conversion numbers.
Formula
Value in target unit = Value in source unit × (Conversion factor of source unit to joules) ÷ (Conversion factor of target unit to joules) Key factors: 1 cal (thermochemical) = 4.184 J 1 kcal = 4,184 J 1 kWh = 3,600,000 J 1 BTU = 1,055.06 J 1 eV = 1.60218 × 10⁻¹⁹ J 1 ft·lbf = 1.35582 J
Pro tips
- When working with food or nutrition data, always confirm whether 'calorie' means small cal (chemistry) or kcal (food labels) — the difference is a factor of 1,000 and the most common source of large conversion errors.
- For electricity cost calculations, convert all appliance energy figures to kWh before multiplying by your utility rate ($/kWh), since power ratings are often given in watts but billing is always in kWh.
- If you're converting between BTU and kWh for HVAC purposes, remember that BTU/hr is a power rate, not a total energy — convert to kWh by dividing BTU/hr by 3,412 to get kilowatts, then multiply by hours of operation.
- When dealing with very large or very small numbers (such as eV or MJ), use scientific notation input to avoid transcription errors — dropping even one zero changes your result by an order of magnitude.
- For cross-checking results, memorize one anchor relationship: 1 kWh ≈ 3,412 BTU ≈ 860 kcal ≈ 3.6 MJ. If your converted answer doesn't roughly match this chain, re-examine your source unit definition.
Key terms
- Joule (J)
- — The SI unit of energy, equal to the work done by a force of one newton acting through one meter; every other energy unit converts to and from joules using a fixed ratio.
- Calorie (cal) vs. Kilocalorie (kcal)
- — A small calorie (cal) is the energy to raise 1 g of water by 1 °C (4.184 J), while a kilocalorie (kcal) equals 1,000 cal and is the unit behind 'Calories' listed on food nutrition labels.
- Kilowatt-Hour (kWh)
- — A unit of electrical energy equal to 3,600,000 joules, representing the energy used by a 1 kW device operating continuously for one hour; the standard unit on electricity bills.
- BTU (British Thermal Unit)
- — An imperial unit of heat energy (≈ 1,055.06 J) defined as the energy needed to raise one pound of water by 1 °F, commonly used in HVAC ratings and US natural gas billing.
- Electron Volt (eV)
- — An extremely small unit of energy (≈ 1.602 × 10⁻¹⁹ J) equal to the kinetic energy gained by one electron accelerating through a one-volt potential difference, used in atomic and particle physics.
- Conversion Factor
- — A precise numerical ratio that relates any given energy unit to the joule, enabling accurate conversion between any two units by multiplication or division without introducing rounding error.
