Unwrap the circle into a flat plane. I will use metric. Your diameter is 1,600 mm, & I will assume a 20 dia bar. The effective (mean) diameter is 1,620 mm with one spiral advance of 150 mm. The bar length is calculated by the pythaggie theorem.
= sqrt(1620^^2 + 150^^2)
= 1,627 mm
That is the length of one loop. Rest of calcs as per RWF7437 above.