The cost for a single traveler on DCL, whether paying cash or using points, is 1 1/2 times the cost for the first/second passenger. So, if the chart says the cost for the 1st/2nd passenger is 150 points, a single traveler would pay 225. It is called a single supplement.
Since this question has come up a couple of times recently, I placed a call to make sure my information is most accurate.
Almost all of the time the single supplement to cruise on points with DCL will be 1.75% or one full adult rate and three-fourths of a second adult rate.
This can vary a little bit by cruise date selection. But the most typical amount is 1.75%