Funny you both agree on something that is incorrectamundo.
Horsepower = Torque x RPM / 5,252
It's also why torque and HP always cross at 5,252 RPM
Revolutions per minute is the angular speed from which the torque is measured.
This sums up both our positions.
From Power Test Dyno:
We know that Work is achieved when there is Force and Displacement. Power is Work factored by Speed(SPEED). Since we are dealing with rotary motion it is called Angular Speed and it is expressed in Radians/sec or Revolutions/Minute. A radian is an angle where the radius is the same length as the length of the arc created by that angle. It is the same no matter the size of the circle. Hence, there are 2π radians in every revolution. Just like a revolution, radians have no unit of measure, which works out well because torque already has the displacement unit (feet) in it.
Other descriptions if you really want to split hairs.
Watt was working in a mine, using horses to pull wagons of coal. He wanted to determine how much coal a pony could pull in a wagon over a given length. He measured how many feet a horse could pull 22,000 pounds of coal in one minute. He then increased that amount to 33,000 foot-pounds in a minute, and called it horsepower.
1 hp = 750 watts, or you can calculate hp from elapsed time
Horsepower = Weight/(ET/5.825)3 This one uses vehicle speed since that's what you thought speed in my previously posted formula represented.