Interesting...according to this system, the clothing size is inversely proportional to the number. My Roman numeral familiarity is a bit rusty, I'm not sure there is a number bigger than M (excepting MM, etc.) Also brings up issues for former XS, as well as XM.

Following this admittedly short numeric trend, the value of the "S" could be 38750.

Reasoning: 50 is 125% of the preceding number (40), and 1000 is 2000% of the preceding number (50), an increase of 1875% between the two deltas. Thererefore, assuming the rate of increase of the delta values is constant, the next increase would be by 3875% of 1000, or 38750.

Therefore, "small" clothing should be labeled "MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMDCCL" instead.

I'm not quite sure what to think of your reasoning [brettjs], and I think your 38,750 is a bit high. Just plot what is given and derive a polynomial, assuming the change from size to size is one step. Setting xl=1, l=2, m=3, so s=4, plug 4 back into the poly equation you derived and your result should be around 2,890 (MMDCCCXC I think). Based on the poly eq of 470x^2 -1400x + 970. Better results from higher order polys, but I'll leave that to you.

If I don't stop now I'll reveal the link between Roman numerals, Fibonacci numbers, fractals, Phi, the Egyption pyramids and world peace...