Hi,

I am not an expert in Design Of Experiments but I don't think that there is a one-fits-all answer to the sample size. You need to have some estimations about your specimens before you can calculate a sample size: approximate mean value, approximate standard deviation, do you values roughly follow a normal distribution?

And you have to choose if you are interested in a confidence interval or a tolerance interval.

I posted a similar question this week. You might want to take a look at the answers in this thread:

http://www.talkstats.com/threads/ho...tween-predefined-upper-and-lower-limit.74001/
Yes, see reply to katxt, but I have mean, stdev from historical data roughly normal.

... that thread was surprisingly enlightening. Thank you, I learned the difference between confidence interval and tolerance interval. In this instance,

**I want to be using a tolerance interval.**

*Definition of a tolerance interval*
A confidence interval covers a population parameter with a stated confidence, that is, a certain proportion of the time. There is also a way to cover a fixed proportion of the population with a stated confidence. Such an interval is called a

*tolerance interval.* The endpoints of a tolerance interval are called

*tolerance limits*. An application of tolerance intervals to manufacturing involves comparing specification limits prescribed by the client with tolerance limits that cover a specified proportion of the population.

*Difference between confidence and tolerance intervals*
Confidence limits are limits within which we expect a given population parameter, such as the mean, to lie. Statistical tolerance limits are limits within which we expect a stated proportion of the population to lie.

**Despite how enlightening that was, my original question still stands.**