hi

does anyone have answer to how to define nr. of layers to obtain desired strength of object.

i would like to do seat post tube for my MTB.
so how to define what would be the minimum amount of layers that tube will still support my weight and not to have too much of not needed weight.

i know there is no 100% accurate way, but at least a point to start

Typically 1000g of carbon used with vacuum or shrink tape is 1mm so you would need around 2000g for 2mm.

7 x 100g is just 700g and less than 1mm thick, not very strong especially if this is not the usual pre preg that most tubes are.