To calculate the right macronutrient ratio for muscle gain, first determine your daily calories (based on body weight, activity level, and goal of lean bulking), then set protein at about 1.6–2.2 g per kg of body weight, fats at around 20–30% of total calories, and fill the remaining calories with carbohydrates for energy and training performance. Key factors include body weight (heavier or leaner individuals need adjusted intake), activity level (more training = higher carbs/calories), and goal (lean gain vs. bulk). A common effective muscle-building breakdown is roughly 30–35% protein, 40–50% carbs, and 20–25% fats, which supports muscle recovery, strength, and sustained energy, though exact ratios should be adjusted based on progress, metabolism, and training intensity.