Joules to Watts Converter
Energy and power are not the same unit — this converts between them using the time involved.
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Your details
Result
- Power
- 60 W
- Energy
- 3,600 J
- In kilowatt-hours
- 0.001 kWh
- In calories
- 860.4207 cal
- Over
- 60 seconds
0.06 kW
3.6 kJ
The unit an electricity meter records
0.860421 food Calories
3600 J spread over 60 s…
1 watt = 1 joule per second, so W = J ÷ s
3600 ÷ 60
60 W
Formula — written step by step
3,600 joules delivered over a minute…
1 watt = 1 joule per second, so W = J ÷ s
A minute is 60 seconds
3,600 ÷ 60
60 W
Joules measure energy — a quantity. Watts measure power — a rate. Converting between them is impossible without a time, which is why this page asks for one rather than offering a factor.
A worked example
What a kettle actually costs to boil
- Kettle
- 2,200 W
- Time to boil
- 3 minutes — 180 s
- Electricity
- 0.28 per kWh
- Energy = 2,200 × 180 = 396,000 J
- 396,000 ÷ 3,600,000 = 0.11 kWh
- 0.11 × 0.28
About 3.1 pence or cents per boil
The 2,200 W on the label is a rate, not a cost — it says nothing until multiplied by a time. This is exactly why bills are in kilowatt-hours: a kilowatt-hour is a quantity of energy, being one kilowatt sustained for one hour, or 3.6 million joules.
How to use this calculator
- Choose which direction you are converting: energy to power, or power to energy.
- Enter the value and the period it applies over — the period is what makes the conversion possible at all.
- Read the kilowatt-hour row when comparing against an electricity bill.
- The calorie row uses the thermochemical calorie; the food Calorie beside it is a thousand of those.
A quantity and a rate
Energy is a quantity, measured in joules. Power is the rate at which energy is delivered or used, measured in watts, and one watt is exactly one joule per second. They are related the way distance and speed are related: you cannot convert kilometres into kilometres per hour without knowing how long the journey took.
That is why this page asks for a period. A converter offering a fixed factor between joules and watts would be answering a question that has no answer.
Reading an appliance label
The wattage printed on an appliance is its rate of consumption while running. A 2,000 W heater uses energy four times as fast as a 500 W one, but which costs more over a day depends entirely on how long each runs.
Electricity is billed in kilowatt-hours precisely because a rate alone cannot be charged for. One kilowatt-hour is a kilowatt sustained for an hour — 3.6 million joules — and it is the natural unit for a quantity of energy at household scale, where a joule is far too small to be useful.
Calories, Calories and the capital letter
The calorie has two meanings that differ by a factor of a thousand. The small calorie is 4.184 joules, the energy to warm one gram of water by one degree Celsius. The food Calorie, written with a capital C, is a kilocalorie — 4,184 joules.
Nutrition labels use the large one, almost always without the capital, which is why a chocolate bar showing "250 calories" is really 250,000 small calories, or about a million joules. Both figures are shown here so the distinction is visible rather than assumed.
Formula & methodology
What this calculator assumes
- Assumes the power is constant over the period. A varying load gives an average, not an instantaneous figure.
- The calorie shown is the thermochemical calorie, exactly 4.184 J. The food Calorie is a kilocalorie, 4,184 J.
- Mechanical horsepower is used, 745.6998715822702 W, not metric horsepower which is about 735.5 W.
Sources
Energy and power units side by side
| Quantity | Unit | Equals | Is a |
|---|---|---|---|
| Energy | joule (J) | 1 W for 1 second | Quantity |
| Energy | kilojoule (kJ) | 1,000 J | Quantity |
| Energy | watt-hour (Wh) | 3,600 J | Quantity |
| Energy | kilowatt-hour (kWh) | 3,600,000 J | Quantity |
| Energy | calorie (cal) | 4.184 J | Quantity |
| Energy | Calorie (kcal) | 4,184 J | Quantity |
| Power | watt (W) | 1 J per second | Rate |
| Power | horsepower (hp) | 745.7 W | Rate |
Everything above the line is an amount; everything below is a speed of delivery. A watt-hour is a power multiplied by a time, which is why it belongs in the energy half despite the name.
Frequently asked questions
How many joules is a watt?
The question has no single answer — a watt is a rate, a joule is a quantity. One watt delivers one joule every second, so a watt sustained for an hour is 3,600 joules.
What is a kilowatt-hour in joules?
3,600,000 J. It is one kilowatt sustained for one hour, and it is the unit electricity meters record.
Is a food Calorie the same as a calorie?
No. A food Calorie is a kilocalorie, a thousand small calories, or 4,184 joules. Labels rarely make the distinction visible.
How does horsepower relate to watts?
One mechanical horsepower is 745.7 W. Both are rates, so they convert directly with no time needed.