Energy Converter
Convert between joules, calories, kWh, BTU and electronvolts.
Convert between joules, calories, kWh, BTU and electronvolts.
This free Energy Converter from KX Toolkit is part of our all-in-one online toolkit. It runs entirely in your browser, so your data never leaves your device for client-side operations. 100% free, forever - no paywall, no credit card, no trial.
How to use the Energy Converter
- Pick the unit you have and the unit you want.
- Enter the value.
- Read the converted value - most tools update as you type.
- Use the swap button to reverse the direction if needed.
What you can do with the Energy Converter
- Convert recipe ingredients between metric and imperial.
- Translate engineering specs across systems.
- Check shipping weights and dimensions before ordering.
- Quick travel conversions for distance, speed and currency.
Why use KX Toolkit's Energy Converter
- Browser-based: Works on Windows, macOS, Linux, iOS and Android - no install, no extension.
- Privacy-first: Client-side tools never upload your data; server-side tools delete files right after processing.
- Mobile-friendly: Full feature parity on phones and tablets - not a stripped-down view.
- Fast: Optimised for instant feedback. No artificial waiting screens, no email-gated downloads.
- One hub for everything: 300+ tools across SEO, text, image, PDF, code, color, calculators and more - skip switching between sites.
Tips for the best results
For very large or very small numbers, use the scientific-notation option - it avoids floating-point rounding errors.
Related Unit Converter Tools
If you find this tool useful, explore the full Unit Converter Tools collection or browse our complete tool directory. KX Toolkit is built for marketers, developers, designers, students and anyone who needs a quick utility without signing up for yet another SaaS.
How do I convert kilowatt-hours to joules?
Multiply kWh by 3,600,000 to get joules. So 1 kWh equals 3.6 MJ, and 100 kWh on your electric bill is 360 MJ of energy delivered. The factor is 1,000 watts times 3,600 seconds per hour. The kWh is the most common billing unit for electricity, while the joule is the SI unit used in physics.
What is a calorie versus a kilocalorie?
A calorie (cal) is the energy needed to raise 1 g of water by 1 C, which is 4.184 J. A kilocalorie (kcal) is 1,000 calories or 4,184 J. Food labels say "calories" but actually mean kilocalories. So a 200 calorie cookie is 200 kcal or 836 kJ. The converter switches between cal, kcal, J, and kJ to clear up the confusion.
How big is a BTU?
One British Thermal Unit (BTU) equals 1,055.06 J or about 252 calories. It is the energy needed to raise one pound of water by 1 F. BTUs are used in heating, ventilation, and air-conditioning specs, especially in the US. A typical room AC unit is rated at 5,000-12,000 BTU/hr, which the power converter can translate into watts.
What is an electronvolt?
An electronvolt (eV) is the energy gained by an electron crossing a 1-volt potential difference, which equals 1.602 x 10^-19 J. It is used in physics and chemistry for atomic and subatomic processes. Visible light photons are about 1.5-3 eV. The converter handles eV alongside the macroscopic units when working with spectroscopy or particle physics.
How much energy does it take to boil water?
Heating 1 kg of water from 20 C to 100 C takes about 334 kJ, then turning it to steam at 100 C takes another 2,260 kJ. So a full kettle (1 L) needs roughly 360 kJ, or 0.1 kWh, just to reach boiling. Real kettles use slightly more because of heat lost to the kettle body and air.
Which energy unit should I use?
Use joules for physics, kilowatt-hours for electricity bills, kilocalories for food, BTUs for HVAC in the US, and electronvolts for atomic-scale work. The converter shows all of them at once, so you can pick whichever is convenient. For engineering work, prefer SI units (joules, kJ, MJ) to avoid mixing systems and creating errors.
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