Hello. Classic fit (regular fit) shirt and slim fit shirt patterns are not the same. Classic fit shirts are designed with a wider cut and offer a more relaxed feel, while slim fit shirts are tailored for a tighter, more contoured fit. Classic fit shirts typically allow for greater freedom of movement through their more relaxed fit in the shoulders, chest, and waist. Slim fit shirts, on the other hand, show your body lines more clearly and offer a more modern look. If you share your height and weight information, I can recommend the most suitable size for you. We wish you pleasant shopping.