What are the usual quantities people usually buy for US stocks, especially for those stocks that is priced at USD$100 per share?

Hi for me I do a little math to find out how much the average cost will be after commission.

Since I use FSMOne its a $10 flat fee, hence if I'm getting 4 shares of a $100 share the average cost per share will be $102.5.

Hence to lower your average cost maybe $1000 is a good amount.

I think especially now with low cost brokers and fractional shares (for some), it really just boils down to personal preference. What would be more important would probably be sizing it appropriately against your portfolio (i.e. how much % of your portfolio is it going to take up and are you comfortable with that?)

That being said, for my own portfolio, usually I open a position with around USD 2k, so at USD 100 per share, that would come up to around 20 shares!​​​