T-shirt sizes can vary depending on the brand, country, and even personal preference. Generally, T-shirt sizes are indicated by letters such as S (Small), M (Medium), L (Large), XL (Extra Large), and so on. However, these letters alone do not provide precise measurements. The same letter size might have different measurements depending on the brand or manufacturer.
For 18-year-old guys with a normal physique, the most common T-shirt size would likely be either Small (S) or Medium (M), depending on their height, weight, and body shape. Some guys may prefer a more fitted look and opt for a smaller size (like S), while others might prefer a looser fit and go for a size M.
To find the best-fitting T-shirt size, it's essential to check the specific sizing chart provided by the brand or manufacturer. This chart typically includes measurements for chest width, shirt length, and sometimes other dimensions to guide you in selecting the right size.
If you're buying a T-shirt in-store, you can try different sizes to see which one fits and feels the most comfortable. And if you're shopping online, be sure to refer to the brand's sizing information and consider reading customer reviews for insights on how the T-shirt fits on individuals with similar physiques.