A good golf polo balances two ideas that can seem opposite: a clean silhouette and unrestricted movement. Size labels are useful, but the way a shirt sits on your body matters more than the letter on the tag.
Start at the shoulders
The shoulder seam should land close to the edge of your shoulder. If it falls far down the arm, the shirt may look oversized. If it sits high and creates tension across the upper back, the polo is likely too small. Rotate your arms slowly and check that the fabric follows rather than resists.
Check the chest and waist
You should be able to pinch a modest amount of fabric at the chest without creating a large fold. Buttons should lie flat, and the placket should not pull open. Through the waist, choose the shape that matches how you wear the shirt. A closer fit works well untucked, while a little extra length and ease can be more comfortable for a tucked look.
Use a swing test
Reach forward, turn into a backswing and finish with your hands high. Watch the hem and sleeves. A small amount of movement is normal, but the shirt should not bind under the arms or rise so far that it needs constant adjustment. Stretch fabric helps, yet correct sizing still does most of the work.
When between sizes
Choose the larger size for a relaxed fit or when your chest measurement is near the upper edge of the chart. Choose the smaller only if you prefer a trim silhouette and still have full movement. Compare your body measurements with the Bloomix size guide on the product page, and remember that different garment categories can fit differently.