My chest and my arm length are two very different sizes. Which size shirt should I choose?

Your best bet is to choose the size of shirt that corresponds to the measured circumference of your chest. For example, size 3XL corresponds to a chest circumference of 118 cm. Your arms will fit that shirt correctly if their length is 80 cm. Please note: always measure arm length from your neck to the end area of your wrist (this measurement should correspond to the desired length of your sleeves).