Tube method to me is 2 strips of fabric (usually WOF) sewn on both sides then cut in a triangle from each sewn edge.
Rough estimate is minus 1/2 inch the width of the strip is the size of the 1/2 square triangle.
If you start with a 4 1/2 inch strip your square will be 4 inches UNFINISHED.
3 inch strip will make a 2 1/2 inch UNFINISHED square.....
Does this help?