ON Serious Mass 12LB

Optimum Nutrition Serious Mass – 12LB Mass Gainer Formula

Built for hard gainers and serious athletes, ON Serious Mass delivers a powerful calorie-dense formula to fuel muscle growth, support recovery, and help you hit your size goals faster. Each serving packs 50g of protein, 254g of carbohydrates, and 1,250 calories — everything your body needs to grow.

Why Serious Mass?

• 50g Protein per serving — supports muscle building and repair
• 1,250 Calories — ideal for high-calorie bulking phases
• 254g Carbohydrates — replenishes glycogen stores and fuels training
• 12LB / 5.44kg bag — 16 servings of serious fuel
• Trusted by athletes in 100+ countries for 35+ years

Who Is This For?

• Hard gainers looking for easy calories to add to their bulking routine
• Athletes in high-volume training or bulking phases
• Anyone needing a convenient, high-calorie protein supplement

Nutrition Highlights (per 2-scoop serving)

• Calories: 1,250
• Protein: 50g
• Carbohydrates: 254g
• Fat: 4g
• Sodium: 510mg

Manufactured in the USA by Glanbia Performance Nutrition. Always refer to the product label for complete nutrition facts, allergen information, and usage guidelines.

Shop the full Optimum Nutrition lineup or browse all Mass Gaining Proteins. Want to learn more? Read our Complete Buying Guide to Protein Powders in Canada.