Energy Converter
Convert Joules, Calories, and kWh. Plus, see how much exercise burns off that donut.
Science & Electrical
Standard Electric Bill Unit
Food & Thermal
Standard Nutrition Label Calorie
Kinetic Context
Explore More Unit Converters
Understanding the Pulse of the Universe
Energy is the currency of the physical world. Whether it's the chemical potential in a sandwich (Calories), the electrical flow charging your car (kWh), or the kinetic impact of a moving object (Joules), it's all the same stuff in different packages. The FreeTools Energy Converter helps you translate between these worlds instantly.
Advanced Tool Features
Food Mode
A dedicated 'Burn It Off' calculator. See how many minutes of running or walking it takes to burn off that pizza slice.
Electrical Math
Convert kWh to Joules instantly. Essential for understanding electric bills and battery capacities.
Kinetic Context
Don't just see numbers. Visualize energy as "Equivalent to lifting 10kg" or "AA Batteries".
SI Standard
We treat the Joule as the master unit, ensuring scientific accuracy for all conversions.
Power vs Energy
Clear distinction between Power (Watts) and Energy (Watt-hours) to prevent common calculation errors.
Deep Learning
Comprehensive guides on eV, BTU, and the physics of work done.
How to Use the Energy Converter
- Use Presets: Tap "AA Battery" or "Candy Bar" to instantly load common energy values.
- Converter Tab: Type a value in Joules, Wh, or Calories. All other units update automatically.
- Food Mode: Switch to the 🍔 tab. Enter the calories of a meal to see how long you need to run, cycle, or walk to burn it off.
- Check Visuals: Look at the dark "Kinetic Context" box to see what your entered energy is capable of (e.g., "Lifting 10kg").
Conversion Formulas Cheat Sheet
| Conversion | Formula | Example |
|---|---|---|
| Food Calories (kcal) to Joules | kcal × 4,184 | 100 kcal × 4184 = 418,400 J |
| kWh to Joules | kWh × 3,600,000 | 1 kWh = 3.6 MJ |
| BTU to Joules | BTU × 1,055 | 10 BTU × 1055 = 10,550 J |
| Electronvolts to Joules | eV × 1.602e-19 | Tiny! |
Common Mistakes to Avoid
- Calories vs Kilocalories:
This is the #1 error. A "Calorie" on a snack wrapper is actually a Kilocalorie (kcal). 1 kcal = 1000 scientific calories (cal). Don't mix them up!
- Power vs Energy:
Watts (W) is Power. Watt-hours (Wh) is Energy. You can't convert Watts to Joules without knowing the time involved.
Pro Tips for Energy Math
- The 4.2 Rule.
For quick mental math, remember that water holds ~4.2 Joules per gram per degree. Useful for heating calculations.
- 3.6 Million.
Memorize that 1 kWh = 3.6 Million Joules. It makes comparing your electric bill to other energy sources much easier.
Energy Reference Guide
| Source | Approx Energy | Joules | Context |
|---|---|---|---|
| AA Battery | 2.8 Wh | ~10,000 | Device Power |
| Rifle Bullet | - | ~3,000 | Kinetic Energy |
| Smartphone Charge | 15 Wh | 54,000 | Daily Use |
| Slice of Bread | 70 kcal | 293,000 | Metabolic Fuel |
| 1kg of TNT | 1000 kcal | 4,184,000 | Explosive |
| Lightning Bolt | 1,400 kWh | 5 Billion | Nature's Power |
Frequently Asked Questions
Expert answers to your energy questions.
What is the difference between cal and kcal?
This is the most common confusion in energy math. In physics, 1 calorie (cal) is the energy to heat 1g of water by 1°C. In nutrition, we use Kilocalories (kcal), which is 1,000 chemistry calories. When a food label says '200 Calories', it actually means '200 kilocalories'.
How many Joules are in 1 kWh?
One Kilowatt-hour (kWh) equals 3.6 million Joules (3,600,000 J). Since a Joule is a very small unit (like a drop of water), utility companies use kWh (like a bucket) to measure electricity usage on your bill.
How much energy is in a AA battery?
A standard alkaline AA battery holds about 2.6 to 3.0 Watt-hours (Wh) of energy, which translates to roughly 9,360 to 10,800 Joules. You would need about 350 AA batteries to equal 1 kWh of electricity.
How many calories to burn 1kg of fat?
To lose 1 kilogram of body fat, you need a calorie deficit of approximately 7,700 kcal. To lose 1 pound of fat, the number is roughly 3,500 kcal. This is why weight loss takes time and consistency.
What is the difference between Power (kW) and Energy (kWh)?
Think of it like water in a hose. Power (kW) is the speed of the water flowing right now (the rate). Energy (kWh) is the total amount of water that filled the bucket over time (the volume). A 1000W microwave running for 1 hour uses 1 kWh of energy.
What is a BTU?
BTU stands for British Thermal Unit. It is the energy needed to heat 1 pound of water by 1°F. It is primarily used in the US for rating heaters, air conditioners, and BBQ grills. 1 BTU ≈ 1,055 Joules.
How much energy is in a lightning bolt?
A single bolt of lightning contains a massive amount of energy, estimated between 1 billion and 5 billion Joules. That's roughly enough energy to power an average American home for about a month, released in a fraction of a second.
Does a phone charger use energy when not plugged in?
Yes, but a negligible amount. Modern chargers draw 'Vampire Power' when idle, usually less than 0.1 Watts. Leaving it plugged in 24/7 for a year costs less than a few cents, though unplugging is still better for the environment.
How many Joules in a gallon of gasoline?
Gasoline is incredibly energy-dense. One gallon of gasoline contains about 132 million Joules (132 MJ) or roughly 36.6 kWh. This explains why electric cars (which are efficient) can travel so far on a relatively small battery compared to a gas tank.
What is an Electronvolt (eV)?
An Electronvolt is a tiny unit of energy used in atomic physics. It is the energy gained by an electron accelerating through 1 volt. It is so small that 1 Joule = 6.2415 × 10^18 eV.
Is 'Calorie' measuring heat or energy?
Both! They are the same thing. Heat is just a form of energy transfer. The original definition of a calorie was based on heating water. Your body 'burns' food to generate heat (body temperature) and do work (moving muscles).
How to convert Joules to Calories quickly?
Divide Joules by 4.184 to get small calories (cal). Divide by 4,184 to get food Calories (kcal). A handy rule of thumb: 4.2 Joules ≈ 1 calorie.