Start with the shoulders, because they reveal everything. The shoulder seam should end roughly where your shoulder ends, not down on your biceps and not high toward the neck. If the seam drops too low, the T-shirt is too large and visually softens the top of the frame. If it sits too high, the fabric will pull across the back and around the underarms, and after a few washes it may lose shape.
The second point is the sleeve. In an elegant-casual look, the sleeve should end roughly mid-bicep so the arm looks proportionate. A sleeve that is too long gives a at-home T-shirt vibe, and one that is too short can be awkward because it exposes the underarm with every movement. If you wear a T-shirt under a blazer, the sleeve must not create a bulky ridge under the arm, because the blazer will start to lift and lose its line.
The third element is length. The safest option is when the T-shirt ends around mid-fly height on your trousers. That way you can wear it untucked, but also tuck it in without stress when the situation calls for it. With classic trousers, a tucked-in T-shirt often looks better because it emphasises the waist and tidies the line. Only then the length needs to be sensible, so the T-shirt does not come out the moment you bend down.
At Albione we have clients with very different body types, and this is a good moment to say something honestly: there is no single ideal fit for everyone. A man with broad shoulders and a narrower waist can go for a more fitted T-shirt, because the fabric will work in his favour. Someone with a fuller stomach should look for a fit that does not cling at the midsection, but also does not turn into a tent. In such cases, a more stable knit often works better, because it highlights less.
If you are building a smart-casual look, try a simple formula: a plain T-shirt, chinos and a blazer. For example, a white T-shirt like Koszulka Victor plus a navy blazer, for instance from the Marynarki line, creates a clean, grown-up effect. It is an outfit you can wear to a client meeting if your industry does not require a tie, and it still does not look like a random combination.