Model Reference (180cm / 73kg): Wearing size XL. The dropped shoulders are distinct, sleeve length hits near the elbow, and the shirt ends just above the hips, achieving a perfect loose vibe suitable for comfort and daily City Boy style.
Estimation (175cm / 65kg): Size L for a similar loose fit to the model. Size M for a snugger, Clean Fit proportion.
Estimation (165cm / 55kg): Size S. Given the longer length, tucking the hem into high-waisted bottoms or wearing platform shoes is recommended to redefine the waistline and overall proportions.