You sound average-sized, if you can confidently say shirts are standard in size. I know a lot of guys who have a hard time finding shirts that fit.
Shirts, jeans, sweaters, anything... they're all over the place in terms of fit.
With shirts, you've got different torso widths, lengths, arm hole sizes (I don't know the word), depths and widths of the neck hole. A slim fit, an athletic fit, a relaxed fit, will all vary from brand to brand.
With jeans, same thing.
Then you've got the fabric and stitching. I'm not sure I'd buy clothes online. Too many variables.
Shirts, jeans, sweaters, anything... they're all over the place in terms of fit.
With shirts, you've got different torso widths, lengths, arm hole sizes (I don't know the word), depths and widths of the neck hole. A slim fit, an athletic fit, a relaxed fit, will all vary from brand to brand.
With jeans, same thing.
Then you've got the fabric and stitching. I'm not sure I'd buy clothes online. Too many variables.