Calculate power, work, or time from any two known values for total change in work (J), time in seconds, and power in watts using any two inputs.
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Power Formula
The power calculator uses the relationship between work, time, and power. Enter any two values and leave the value you want to find blank.
P = W/t
W = P*t
t = W/P
- P = power, measured in watts (W)
- W = total change in work or energy transferred, measured in joules (J)
- t = time, measured in seconds (s)
If you enter work and time, the calculator finds power by dividing work by time. If you enter power and time, it finds total work by multiplying power by time. If you enter work and power, it finds time by dividing work by power.
Common Power Unit Relationships
Power is most often shown in watts, but larger or mechanical systems may use kilowatts or horsepower.
| Unit | Equivalent | Notes |
|---|---|---|
| 1 watt | 1 joule per second | The base SI unit of power |
| 1 kilowatt | 1,000 watts | Common for appliances and electrical systems |
| 1 horsepower | about 746 watts | Often used for engines and motors |
Typical Power Values
| Example | Approximate Power | Meaning |
|---|---|---|
| Small LED bulb | 5 to 15 W | Low energy transfer rate |
| Laptop charger | 45 to 100 W | Moderate electrical power |
| Microwave oven | 700 to 1,200 W | High energy transfer rate |
| Electric kettle | 1,000 to 1,500 W | Common high-power household device |
Example Problems
Example 1: Find power
You do 600 joules of work in 20 seconds. Find the power.
P = W/t
P = 600/20 = 30
The power is 30 watts.
Example 2: Find work
A machine runs at 250 watts for 12 seconds. Find the total work done.
W = P*t
W = 250*12 = 3000
The total work is 3,000 joules.
FAQ
What does one watt mean?
One watt means one joule of work or energy transferred each second. For example, a power value of 50 watts means 50 joules are transferred every second.
Can time be zero in the power formula?
No. Time cannot be zero when calculating power because the formula divides by time. Dividing by zero is undefined. Use a positive time value in seconds.
Is work the same as energy in this calculator?
For this calculation, work and energy transfer use the same unit, joules. The calculator treats the work value as the total amount of energy transferred over the given time.
