15 Watts to Joules
Watts measure power and joules measure energy, so the answer depends on time. Here is what a 15 W device uses over each period.
15 J per second
Because 1 watt = 1 joule per second, 15 W delivers 15 J every second it runs.
- Per minute
- 900 J
- Per hour
- 54,000 J
- Per hour (kWh)
- 0.015 kWh
- Per day
- 1,296,000 J
15 watts to joules, explained
A watt is a rate: one watt means one joule of energy is used every second. So 15 watts means 15 joules per second. To get a total number of joules you multiply by how long the power runs.
For example, a 15 W device left on for one hour uses 15 × 3,600 = 54,000 J. Over a full day it uses 1,296,000 J. On an electricity bill, one hour of use is 0.015 kWh.
15 W draws about 25% of the power of an old-style 60 W incandescent bulb. One hour at 15 W consumes 0.015 kWh of electricity — about 0.22¢ at a US average residential rate of $0.15 per kWh.
joules = 15 W × time in secondsWi-Fi Router (15 W)
Household broadband internet router/modems draw about 15 watts of continuous, non-stop power.
Electrical Power Comparison Scale
Need a different power or time? Use the interactive converter below for any combination.
15 W energy over time
| Time on | Energy (joules) |
|---|---|
| 1 second | 15 J |
| 1 minute | 900 J |
| 10 minutes | 9,000 J |
| 1 hour | 54,000 J |
| 6 hours | 324,000 J |
| 1 day | 1,296,000 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: 15 watts
How many joules is 15 watts?
15 watts is not a fixed number of joules on its own — watts measure power and joules measure energy, so you need a time. A 15 W device uses 15 J every second, 54,000 J over one hour (0.015 kWh).
How do you convert 15 watts to joules?
Multiply 15 by the number of seconds the power runs. Joules = 15 × time in seconds. For one hour that is 15 × 3,600 = 54,000 J.
How much energy does a 15 W device use per hour?
A 15 W device running for one hour uses 54,000 J, which is 0.015 kWh on an electricity bill.