Free Online Calculators
Joule, kWh, kcal, BTU and more
This converter instantly transforms energy values between units like Joules, kilowatt-hours, kilocalories, and BTUs. It uses fixed physical conversion factors — for example, 1 kWh equals exactly 3,600,000 Joules. Whether you're working on physics homework, reading a food label, or checking your energy bill, you'll get the right number in seconds.
1 Joule equals 0.001 Kilojoule. The full conversion table for all 10 units is right below the calculator.
| Unit | J | kJ | MJ | cal | kcal | Wh | kWh | BTU | ftlb | eV |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 Joule | 1 | 0.001 | 1.0000e-6 | 0.239006 | 0.000239 | 0.000278 | 2.7778e-7 | 0.000948 | 0.737561 | 6241495961752113000 |
| 1 Kilojoule | 1000 | 1 | 0.001 | 239.005736 | 0.239006 | 0.277778 | 0.000278 | 0.947813 | 737.561033 | 6.241495961752113e+21 |
| 1 Megajoule | 1000000 | 1000 | 1 | 239005.736138 | 239.005736 | 277.777778 | 0.277778 | 947.813394 | 737561.033175 | 6.241495961752113e+24 |
| 1 Calorie | 4.184 | 0.004184 | 4.1840e-6 | 1 | 0.001 | 0.001162 | 1.1622e-6 | 0.003966 | 3.085955 | 26114419103970840000 |
| 1 Kilocalorie | 4184 | 4.184 | 0.004184 | 1000 | 1 | 1.162222 | 0.001162 | 3.965651 | 3085.955363 | 2.611441910397084e+22 |
| 1 Watt-hour | 3600 | 3.6 | 0.0036 | 860.42065 | 0.860421 | 1 | 0.001 | 3.412128 | 2655.219719 | 2.246938546230761e+22 |
| 1 Kilowatt-hour | 3600000 | 3600 | 3.6 | 860420.650096 | 860.42065 | 1000 | 1 | 3412.12822 | 2655219.719432 | 2.2469385462307606e+25 |
| 1 BTU | 1055.06 | 1.05506 | 0.001055 | 252.165392 | 0.252165 | 0.293072 | 0.000293 | 1 | 778.171144 | 6.585152729406184e+21 |
| 1 Foot-pound | 1.35582 | 0.001356 | 1.3558e-6 | 0.324049 | 0.000324 | 0.000377 | 3.7662e-7 | 0.001285 | 1 | 8462345054862750000 |
| 1 Electronvolt | 1.6022e-19 | 1.6022e-22 | 1.6022e-25 | 3.8293e-20 | 3.8293e-23 | 4.4505e-23 | 4.4505e-26 | 1.5186e-22 | 1.1817e-19 | 1 |
Rounded to six significant digits.
An energy converter is a tool that restates one energy value in a different unit, for example joules as kilowatt-hours or calories. The physical amount of energy stays the same; only the unit and the number change.
Multiply power by the time it is applied: energy = power × time. A device drawing 1 kW for one hour uses 1 kWh, so power alone is not energy until you attach a duration.
Energy conversion has two meanings: in physics it is energy changing form, such as electrical energy becoming heat or light, and in everyday calculation it is expressing the same energy in another unit. Unit conversion changes only the notation, not the quantity.
Commonly listed are mechanical to electrical, chemical to thermal, electrical to light or heat, and thermal to mechanical energy. Every real conversion loses part of the input as waste heat.
Multiply by a conversion factor written as a fraction so the old unit cancels out and the new one remains. For energy that means going through joules as a pivot unit.
It is called unit conversion, and the method of cancelling units in a chain of factors is known as dimensional analysis or the factor-label method.
Any converter that shows the conversion factor and keeps full precision works; a browser-based converter needs no install and handles energy units such as joule, calorie, kWh and BTU.
Metric prefixes are powers of ten, so you only move the decimal point: kilo means three places, mega six, milli three the other way. That is why 1 kJ equals 1000 J without any real arithmetic.
Whether you're a student working through physics problems, an engineer calculating power consumption, or just trying to make sense of your electricity bill, our free online energy converter makes it effortless to switch between all major energy units. Convert Joules, kilowatt-hours, kilocalories, British Thermal Units, and many more — instantly and accurately.
Energy is measured in dozens of different units depending on the context. A physicist might work in Joules, a nutritionist in kilocalories, a utility company in kilowatt-hours, and a heating engineer in BTUs. When these worlds overlap — as they often do — you need a reliable way to translate between them. Getting conversions wrong can lead to costly mistakes in engineering projects, dietary miscalculations, or misunderstood energy reports.
Our energy converter eliminates that risk. It handles the math instantly so you can focus on what matters.
Our tool supports a comprehensive range of energy units used across science, engineering, nutrition, and everyday life:
Using our energy converter is straightforward — no registration, no downloads, and no fees required. Here's how it works:
The converter updates in real time as you type, making it fast and frictionless to use on any device — desktop, tablet, or smartphone.
Here are some of the most frequently needed energy conversions our users perform:
Food labels in different countries use different units. In many parts of Europe, energy is shown in both kcal and kJ. Our converter lets you quickly switch between them so you always know exactly how much energy is in what you eat.
Your electricity meter measures consumption in kilowatt-hours. If you need to compare that to gas usage (often listed in BTUs or MJ), our converter bridges the gap instantly. This is especially useful when calculating your home's total energy footprint.
From mechanical work measured in foot-pounds to thermal energy in BTUs, engineers work across multiple unit systems daily. Our converter supports professional-grade accuracy for technical applications.
Physics and chemistry students regularly need to convert between Joules, calories, and electronvolts. Our tool provides instant, accurate results that help you check your work and deepen your understanding of energy relationships.
The SI (International System of Units) unit of energy is the Joule (J). It is defined as the amount of energy transferred when a force of one Newton moves an object one meter in the direction of the force. All other energy units can be expressed as multiples or fractions of Joules.
A calorie (cal) is the amount of energy needed to raise the temperature of one gram of water by 1°C. A kilocalorie (kcal) equals 1,000 calories. Importantly, when food labels say 'Calories' (with a capital C), they almost always mean kilocalories. So a 200-Calorie snack actually contains 200 kcal, or 200,000 small calories.
One kilowatt-hour is equal to 3,600,000 Joules (3.6 MJ). This is because 1 kW equals 1,000 watts (or 1,000 J/s), and one hour contains 3,600 seconds. Multiplying these gives 3,600,000 Joules per kWh.
A British Thermal Unit (BTU) is the amount of heat needed to raise the temperature of one pound of water by 1°F. It's widely used in the United States for measuring heating and cooling capacity — for example, air conditioners and furnaces are rated in BTUs. One BTU equals approximately 1,055 Joules.
Yes, completely. Our energy converter is 100% free with no sign-up, no subscription, and no limits on use. It works directly in your browser on any device, any time you need it.