What is this converter?
Converts energy between joules, kilojoules, calories, kilocalories, watt-hours, and kilowatt-hours. All conversions pass through the joule, the SI derived unit of energy.
Use it when:
- A nutrition label quotes energy in kilojoules and you think in kilocalories, or the reverse.
- You are converting an electricity meter reading in kWh to joules.
- A specification mixes energy units across sources.
Intended for: Anyone reading nutrition labels, energy bills, or equipment specifications.
How is this calculated?
- Each supported unit is defined by a fixed conversion factor relative to one base unit for the quantity (for example, the metre for length).
- The value you enter is first converted from the source unit into that base unit by multiplying by the source unit's factor.
- The base value is then converted into the target unit by dividing by the target unit's factor.
- Because both factors are exact constants, the conversion is a single deterministic multiplication and division — the same input always produces the same output.
Example
Converting 1 kilowatt-hour to joules.
- 1 watt is 1 joule per second.
- One hour is 3,600 seconds, so 1 Wh = 3,600 J.
- 1 kWh = 1,000 × 3,600 = 3,600,000 J.
Result: 1 kilowatt-hour = 3.6 megajoules.
Frequently asked questions
Is a food "calorie" the same as a calorie here?
No, and this is the most common confusion in the list. The Calorie on a nutrition label is a kilocalorie — 1,000 of the calories used in physics. Choose kilocalories when working with food energy.
How do kilojoules and kilocalories relate?
One kilocalorie is about 4.184 kilojoules, so a 2,000 kcal daily intake is roughly 8,368 kJ.
Assumptions
What this converter takes as given:
- Conversion factors are the internationally standardised definitions of each unit, not regional or historical variants.
- The value you enter is treated as an exact quantity — no measurement uncertainty is carried through the conversion.
- Results are rounded only for display; the underlying arithmetic uses full precision.
Limitations
What this converter cannot know or does not model:
- The converter does not know the precision of your original measurement, so it cannot report significant figures for you.
- Units that share a name but differ by region or era (for example, different definitions of a gallon or a ton) are offered only in the variants listed in the unit menu.
- Very large or very small magnitudes are subject to the limits of double-precision floating-point arithmetic.