In SI Units, what is the electrical equivalent of one horsepower? Up to how many horsepower can a single horse deliver?

How is Horsepower Measured?
Watt set out to scientifically compare the two. By determining that a horse could turn a mill wheel with a 24-foot diameter 144 times in an hour, he calculated that a horse could produce 33,000 foot pounds per minute. That is a lot of work! At that time, Watt's steam engine could produce five horsepower, or the amount of work five draft horses could do in a day.

Is a Horse Really One Horsepower?
In Watt's determination of horsepower, he based his calculations off the average rate of work a draft horse could do over one full day. However, one horse does not always produce one horsepower. In fact, over a short period of time a horse can exert up to 14.9 horsepower! The power one horse can produce is affected by that horse's physical fitness and breed.