Hypertrophy Rep Range Calculator
Find the ideal rep range for muscle growth based on exercise type, target muscle, time under tension, and load. Use this when programming workouts to maximize hypertrophy for a specific muscle group.
About this calculator
Muscle hypertrophy is maximized when mechanical tension, metabolic stress, and muscle damage are optimally balanced. Research suggests compound lifts on large muscle groups respond well to 6–12 reps, while isolation exercises on smaller muscles thrive in the 10–20 rep range. This calculator adjusts the base rep range using your time under tension (TUT) goal and your percentage of 1RM. The core formula for compound lifts on large muscles is: reps = clamp(6–12, round(6 + TUT/10 − load%/15)). For isolation exercises: reps = clamp(10–20, round(10 + TUT/8 − load%/12)). Higher TUT goals push reps upward; heavier loads (higher % of 1RM) pull them back down. The result is a personalised rep target that balances stimulus intensity with sufficient time under load for hypertrophy.
How to use
Suppose you are programming a barbell bench press (compound) targeting the pectorals (large muscle), with a TUT goal of 40 seconds and a working load of 75% of 1RM. Using the compound/large-muscle formula: reps = round(6 + 40/10 − 75/15) = round(6 + 4 − 5) = round(5) = 5, then clamped to the minimum of 6, giving a target of 6 reps. Now try a lighter load of 60% 1RM with the same TUT: reps = round(6 + 4 − 4) = 6. With a TUT of 60 s at 60%: round(6 + 6 − 4) = 8 reps — solidly in the hypertrophy sweet spot.
Frequently asked questions
What is the best rep range for hypertrophy according to science?
The classic hypertrophy rep range is roughly 6–12 reps for compound movements and 10–20 reps for isolation exercises, corresponding to moderate loads of 60–80% of 1RM. Meta-analyses (e.g., Schoenfeld 2017) show that a wide range of rep schemes can build muscle provided sets are taken close to failure. However, moderate rep ranges maximize the combination of mechanical tension and metabolic stress that drives protein synthesis. This calculator refines that window further using your personal TUT target and load percentage.
How does time under tension affect the optimal number of reps for muscle growth?
Time under tension (TUT) refers to how long a muscle is under load during a set, typically measured in seconds. Longer TUT increases metabolic stress and accumulates more fatigue within the muscle fibers, both of which are key hypertrophy drivers. A TUT of 40–70 seconds per set is commonly recommended for hypertrophy. In this calculator, a higher TUT goal increases the suggested rep count so the total set duration aligns with that window, provided your load and tempo are consistent.
Should I use different rep ranges for compound vs isolation exercises for hypertrophy?
Yes. Compound movements like squats, deadlifts, and bench press involve multiple joints and recruit large primary movers under high systemic load, making them effective in the 6–12 rep range. Isolation exercises like curls or lateral raises have lower systemic fatigue cost and target smaller muscles that respond well to higher rep ranges of 10–20. Using heavier loads for isolation work often compromises form and shifts tension away from the target muscle, reducing hypertrophic stimulus.