18 Watts to Joules
Watts measure power and joules measure energy, so the answer depends on time. Here is what a 18 W device uses over each period.
18 J per second
Because 1 watt = 1 joule per second, 18 W delivers 18 J every second it runs.
- Per minute
- 1,080 J
- Per hour
- 64,800 J
- Per hour (kWh)
- 0.018 kWh
- Per day
- 1,555,200 J
18 watts to joules, explained
A watt is a rate: one watt means one joule of energy is used every second. So 18 watts means 18 joules per second. To get a total number of joules you multiply by how long the power runs.
For example, a 18 W device left on for one hour uses 18 × 3,600 = 64,800 J. Over a full day it uses 1,555,200 J. On an electricity bill, one hour of use is 0.018 kWh.
18 W draws about 30% of the power of an old-style 60 W incandescent bulb. One hour at 18 W consumes 0.018 kWh of electricity — about 0.27¢ at a US average residential rate of $0.15 per kWh.
joules = 18 W × time in secondsFluorescent tube bulb (18 W)
Small under-cabinet fluorescent bulbs consume around 18 watts of electrical power.
Electrical Power Comparison Scale
Need a different power or time? Use the interactive converter below for any combination.
18 W energy over time
| Time on | Energy (joules) |
|---|---|
| 1 second | 18 J |
| 1 minute | 1,080 J |
| 10 minutes | 10,800 J |
| 1 hour | 64,800 J |
| 6 hours | 388,800 J |
| 1 day | 1,555,200 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: 18 watts
How many joules is 18 watts?
18 watts is not a fixed number of joules on its own — watts measure power and joules measure energy, so you need a time. A 18 W device uses 18 J every second, 64,800 J over one hour (0.018 kWh).
How do you convert 18 watts to joules?
Multiply 18 by the number of seconds the power runs. Joules = 18 × time in seconds. For one hour that is 18 × 3,600 = 64,800 J.
How much energy does a 18 W device use per hour?
A 18 W device running for one hour uses 64,800 J, which is 0.018 kWh on an electricity bill.