20 Watts to Joules
Watts measure power and joules measure energy, so the answer depends on time. Here is what a 20 W device uses over each period.
20 J per second
Because 1 watt = 1 joule per second, 20 W delivers 20 J every second it runs.
- Per minute
- 1,200 J
- Per hour
- 72,000 J
- Per hour (kWh)
- 0.02 kWh
- Per day
- 1,728,000 J
20 watts to joules, explained
A watt is a rate: one watt means one joule of energy is used every second. So 20 watts means 20 joules per second. To get a total number of joules you multiply by how long the power runs.
For example, a 20 W device left on for one hour uses 20 × 3,600 = 72,000 J. Over a full day it uses 1,728,000 J. On an electricity bill, one hour of use is 0.02 kWh.
20 W draws about 33% of the power of an old-style 60 W incandescent bulb. One hour at 20 W consumes 0.02 kWh of electricity — about 0.3¢ at a US average residential rate of $0.15 per kWh.
joules = 20 W × time in secondsStanding box fan (low) (20 W)
A portable box fan running on low speed draws approximately 20 watts.
Electrical Power Comparison Scale
Need a different power or time? Use the interactive converter below for any combination.
20 W energy over time
| Time on | Energy (joules) |
|---|---|
| 1 second | 20 J |
| 1 minute | 1,200 J |
| 10 minutes | 12,000 J |
| 1 hour | 72,000 J |
| 6 hours | 432,000 J |
| 1 day | 1,728,000 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: 20 watts
How many joules is 20 watts?
20 watts is not a fixed number of joules on its own — watts measure power and joules measure energy, so you need a time. A 20 W device uses 20 J every second, 72,000 J over one hour (0.02 kWh).
How do you convert 20 watts to joules?
Multiply 20 by the number of seconds the power runs. Joules = 20 × time in seconds. For one hour that is 20 × 3,600 = 72,000 J.
How much energy does a 20 W device use per hour?
A 20 W device running for one hour uses 72,000 J, which is 0.02 kWh on an electricity bill.