Two people can carry the same piano up the same stairs, but the one who finishes in half the time is twice as powerful. Power is the rate of doing work: power equals work divided by time, P = W / t. The work can be identical — the piano weighs the same, the staircase is the same height — yet the faster mover commands more power, which is why sprinters, tow trucks, and table saws are all rated by it rather than by total work.

This calculator divides your numbers directly. Type the total work into the Work Done (W) box and the elapsed time into the Time (t) box; the Power (P) box returns the rate. A pickup in Colorado winching a 4,000-pound boat up a 30-foot ramp does 120,000 foot-pounds of work — finish in 60 seconds and the Power box shows 2,000 ft-lb/s, which divides by 550 to give about 3.6 horsepower. James Watt defined the horsepower as 550 foot-pounds per second so he could sell steam engines to mine owners, and the unit stuck: your car's rating, your microwave's wattage, and your air conditioner's tons all trace back to this one division.

With the pre-filled defaults — Work Done (W) 100 J, Time (t) 5 s — the Power Calculator (Physics) returns Power (P) 20.0000 W (Watts). Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.