What unit of engine power did James Watt help popularize?

What unit of engine power did James Watt help popularize? James Watt helped popularize horsepower as a way to compare steam-engine output with the work performed by draft horses.

The comparison was a practical sales tool. Watt's improved steam engines competed with machines powered by horses, so expressing output in familiar terms helped customers understand what an engine could replace. He estimated the work a strong “brewery horse” could perform and standardized the figure with Matthew Boulton at 33,000 foot-pounds per minute.

That figure defines one imperial horsepower as approximately 746 watts. Metric horsepower is a different unit, about 735.5 watts, so “horsepower” is not completely uniform across countries or industries. Engine makers may also distinguish brake horsepower, shaft horsepower, boiler horsepower, and other specialized versions.

The unit was not a fundamental SI measurement, and Watt did not literally measure every horse. His estimate was deliberately generous, helping market engines by making their rated performance easy to grasp. The watt, the modern SI unit of power, was later named in Watt's honour.