Suppose that your business is operating at the 4.5 sigma quality level. If projects have an average improvement rate of 50% annually, how many years will it take to achieve six sigma quality? If the business is operating at the 4.5-sigma quality level, then it is producing about 1350 ppm defective. To reach six-sigma quality, it will take x years where x is the solution to 1350(1 -0.5)* Thus, the business will reach six-sigma quality during the eighth month of the 9th year