40 Watts to Joules
Watts measure power and joules measure energy, so the answer depends on time. Here is what a 40 W device uses over each period.
40 J per second
Because 1 watt = 1 joule per second, 40 W delivers 40 J every second it runs.
- Per minute
- 2,400 J
- Per hour
- 144,000 J
- Per hour (kWh)
- 0.04 kWh
- Per day
- 3,456,000 J
40 watts to joules, explained
A watt is a rate: one watt means one joule of energy is used every second. So 40 watts means 40 joules per second. To get a total number of joules you multiply by how long the power runs.
For example, a 40 W device left on for one hour uses 40 × 3,600 = 144,000 J. Over a full day it uses 3,456,000 J. On an electricity bill, one hour of use is 0.04 kWh.
40 W draws about 67% of the power of an old-style 60 W incandescent bulb. One hour at 40 W consumes 0.04 kWh of electricity — about 0.6¢ at a US average residential rate of $0.15 per kWh.
joules = 40 W × time in secondsDesk fan (high) (40 W)
A rotating desk-mounted office fan running on high draws about 40 watts.
Electrical Power Comparison Scale
Need a different power or time? Use the interactive converter below for any combination.
40 W energy over time
| Time on | Energy (joules) |
|---|---|
| 1 second | 40 J |
| 1 minute | 2,400 J |
| 10 minutes | 24,000 J |
| 1 hour | 144,000 J |
| 6 hours | 864,000 J |
| 1 day | 3,456,000 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.
FAQ: 40 watts
How many joules is 40 watts?
40 watts is not a fixed number of joules on its own — watts measure power and joules measure energy, so you need a time. A 40 W device uses 40 J every second, 144,000 J over one hour (0.04 kWh).
How do you convert 40 watts to joules?
Multiply 40 by the number of seconds the power runs. Joules = 40 × time in seconds. For one hour that is 40 × 3,600 = 144,000 J.
How much energy does a 40 W device use per hour?
A 40 W device running for one hour uses 144,000 J, which is 0.04 kWh on an electricity bill.