400 Watts to Joules
Watts measure power and joules measure energy, so the answer depends on time. Here is what a 400 W device uses over each period.
400 J per second
Because 1 watt = 1 joule per second, 400 W delivers 400 J every second it runs.
- Per minute
- 24,000 J
- Per hour
- 1,440,000 J
- Per hour (kWh)
- 0.4 kWh
- Per day
- 34,560,000 J
400 watts to joules, explained
A watt is a rate: one watt means one joule of energy is used every second. So 400 watts means 400 joules per second. To get a total number of joules you multiply by how long the power runs.
For example, a 400 W device left on for one hour uses 400 × 3,600 = 1,440,000 J. Over a full day it uses 34,560,000 J. On an electricity bill, one hour of use is 0.4 kWh.
joules = 400 W × time in secondsNeed a different power or time? Use the interactive converter below for any combination.
400 W energy over time
| Time on | Energy (joules) |
|---|---|
| 1 second | 400 J |
| 1 minute | 24,000 J |
| 10 minutes | 240,000 J |
| 1 hour | 1,440,000 J |
| 6 hours | 8,640,000 J |
| 1 day | 34,560,000 J |
Convert any wattage and time
The full Watts to Joules converter handles W, kW, MW, any time unit, and the reverse joules→watts and time calculations.
Frequently asked questions
How many joules is 400 watts?
400 watts is not a fixed number of joules on its own — watts measure power and joules measure energy, so you need a time. A 400 W device uses 400 J every second, 1,440,000 J over one hour (0.4 kWh).
How do you convert 400 watts to joules?
Multiply 400 by the number of seconds the power runs. Joules = 400 × time in seconds. For one hour that is 400 × 3,600 = 1,440,000 J.
How much energy does a 400 W device use per hour?
A 400 W device running for one hour uses 1,440,000 J, which is 0.4 kWh on an electricity bill.