Energy Converter

Energy unit converter for joules, kWh, calories, and BTU

This energy converter helps you translate a single energy amount into another unit without doing manual constants and calculator math. People run into energy units in electricity bills (kWh), nutrition labels (kcal), heating and HVAC specs (BTU), physics and engineering work (J, kJ, MJ), and even small-scale science and electronics (eV). The problem is simple: the units look familiar, but the scale differences are huge, and it is easy to be off by factors of 1,000 or more.

Use the calculator by entering the energy value you have, selecting the unit it is currently in, then selecting the unit you want. The main result shows the direct conversion. To reduce mistakes and help with intuition, the calculator also displays a breakdown in several common units at the same time. That makes it easier to sanity-check your answer. If you expected a household-sized number, but you got something that looks microscopic, the breakdown usually makes the issue obvious.

The conversion works by translating your input into a single base unit (joules), then converting from joules into the target unit. This method is reliable because every unit has a fixed relationship to joules. For example, watt-hours are energy over time (power multiplied by time), so they can be expressed in joules. Calories and BTU are older heat-based units, but they also map cleanly to joules. When your inputs are correct, the conversion is deterministic and repeatable.

Assumptions and how to use this calculator

• The converter treats values as pure energy amounts. It does not infer power, time, or rate unless you already expressed energy in a unit like Wh or kWh.
• BTU is calculated using the IT definition (commonly used in many references). Other BTU variants exist and may differ slightly.
• Calories use the thermochemical calorie (cal) and kilocalorie (kcal). Food labels often call 1 kcal a "Calorie" with a capital C.
• Therm is treated as a standard US therm (a fixed energy unit). Gas billing can vary by region and may include additional factors beyond raw energy.
• Rounding is applied for readability. If you need maximum precision for scientific work, use more significant figures and avoid rounding early in your workflow.

Common questions

What is the difference between kWh and kW?

kW is power, meaning how fast energy is used or produced. kWh is energy, meaning how much energy was used or produced over time. If a device draws 1 kW for 1 hour, it consumes 1 kWh of energy. This calculator converts energy units, so it deals with kWh, not kW.

Why do I see both calories and kilocalories?

They differ by a factor of 1,000. In nutrition, the "Calorie" printed on labels is usually a kilocalorie (kcal). In physics and chemistry, "cal" may refer to the smaller calorie. If you are converting food energy, choose kcal.

Which BTU should I use?

BTU has a few definitions (for example, IT and thermochemical). Most everyday HVAC references use a conventional BTU close to the IT value. If your source explicitly states a BTU definition, match it. If not, using BTU (IT) is a practical default for general conversions.

What if I do not know the exact unit from my source?

Do not guess. Look for the unit symbol next to the number (J, kJ, MJ, Wh, kWh, kcal, BTU). If the number is on an electricity bill, it is almost always kWh. If it is on a nutrition label, it is usually kcal (Calories). If it is on heating or cooling equipment, it is often BTU per hour (BTU/h), which is power, not energy. Convert BTU/h only after multiplying by time to get BTU.

Why does the breakdown show very small or very large numbers?

Energy units span extreme scales. One kilowatt-hour is 3.6 million joules, and one electronvolt is tiny compared to everyday units. Large or small values are normal. The breakdown exists to help you spot mistakes: if multiple equivalent values do not look consistent, check your input unit and decimal placement.