anybody who has ordered merch from EU, how to convert tshirt sizes to Indian sizes? google confused me even more

I don't have the full answer, but I hope this helps. I used to wear L in India (like size 40) and have been shopping M size in all brands since I have got here.

US: S,   M, L

EU: M,   L, XL

IN: M/L, L, XL

Above is my general observation

so I use S India, I should order S EU. I can get it altered slightly if it runs larger.