There is not a correct answer to this question. Some people will bend 300+ inches of material in 1 piece. Others will think 180 inches is too much for 1 piece. To help decide, ask yourself these questions:
- Is there a good way to 2-piece the shape? Is there a good place for an additional seam?
- Is the shape simple or more complex?
As a guideline, simple shapes can be run in 1 piece. Letters with script may require more than 1 piece
- What is the height of the letter?
As a guideline, letters/shapes that are 36 inches or less should be run in 1 piece.
A 10-foot high capital D can be made in 1 piece. It is a very simple shape with two 90-degree bends and a big arc. Further, there is not a good place for a second seam, as you would not want an additional seam in the middle of the arc or in the middle of the left side.
It may be beneficial to consult the person putting your contour/letter together. They are going to be able to decide which is easier for them – a big piece of material or several pieces of material requiring 2 or more seams.