We had an 8' x 16' wood dock (built with 2x6s) that almost sunk but were able to salvage it. We want to make it a floating dock. I am looking at some marine floats on sale (sale ends today) that are 3'x 4'x 9". If I did all the math correctly I would be like at 39 per sq inch and I guess the norm is 40 to 60.
Has anyone used 9" or should I consider more depth than 9" ones. Would the 9" suffice?
I am currently looking for someone in my area (central Indiana) to do the work vs us tackling it.

Mark:

You have to calculate the weight of the dock plus the weight of the maximum number of people that will be on the dock. Then calculate the volume of water that the floats will displace if they are 99.9% submerged.

The 99.9% figure should ALWAYS exceed the max gross weight of the dock. You can use thicker floats if you want the dock to sit higher up out of the water too.

One cubic foot of water weighs 62.4 pounds.....