There's a chart on the Amazon listing. It suggests MS is a bit smaller than stock L, M is a bit larger.

I went for the M/ML/L 3 size pack, so I can figure it out between the three of them. The stock L is I think still a bit small for me. I suspect I'll want M or ML, haven't got them yet, first order had a delivery problem and I had to order again. Other Azla tips, I use M or ML, while I usually use L in other brand tips.