T-shirts shrink!!!!

I did a  small experiment to see how clothes shrink. I have kind of noticed that many pieces of clothes shank after tumble drying, and they fit tighter and tighter. Did I gain weight or are the clothes getting smaller?

I tried washing and drying this new brown shirt - placed underneath a red shirt for comparison. Before washing, it was as long as the red one, and the sleeves were long too, but after drying, it did shrink!! The chest, length and sleeves all got smaller by 2-4 cm! It was clear by measuring the actual length. It seems that the length are more affected than the width. That means, your shirt will get shorter, and will have shorter sleeves, but chest size may not change as much. 

I cannot do anything with this because it was the most gentle wash and dry cycles I could select. Cotton shirts are especially prone to shrinking. I need to take this into consideration and buy one size larger.