I am trying to find formulae for calculating the overlap between two normally distributed populations.

There are some online calculators specifically for this but they do not have the resolutinion i require.

So for M1,σ1 and M2,σ2, (where M is Mean and σ is StDev) what formula will give me the probability of samples from these populations overlapping.

Im trying to find the % interferance fit between an OD and ID

I have been using JMP so far as a stop gap but i know this is not entirely accurate, the method below is what im using

by finding the % of Group 2 below the point M1+3(σ1) and vise versa, then multiplying the two % (Using CpK analysis)

M+3(σ) still leaves 0.15% of the population unacounted for and i want a more accurate result.

Your comments on a better fast method aswell as the formuala are welcome and appraciated

Thanks