Hypertrophy Rep Range Calculator
Calculate the correct training weight to use for any target rep range based on your one-rep max. Use this when programming hypertrophy blocks to ensure you are lifting at the right intensity for muscle growth.
About this calculator
This calculator uses the Epley-derived load estimation formula to back-calculate the appropriate working weight from your one-rep maximum (1RM) for a given rep target. The formula is: working_weight = one_RM × (1.0278 − 0.0278 × target_reps). This is the inverse of the classic Epley formula (1RM = weight × (1 + reps / 36)), rearranged to solve for weight. For hypertrophy, the scientific consensus places the optimal rep range at 6–12 reps, corresponding roughly to 65–85% of 1RM. Training within this window generates sufficient mechanical tension and metabolic stress — the two primary drivers of muscle growth. Knowing the precise load for your target rep range removes guesswork from programming and ensures you train at the right stimulus intensity rather than relying on feel alone.
How to use
Suppose your one-rep max on the squat is 120 kg and you want to work in the 8-rep hypertrophy range. Step 1: Enter 120 in One Rep Max and 8 in Target Rep Range. Step 2: The calculator computes: 120 × (1.0278 − 0.0278 × 8) = 120 × (1.0278 − 0.2224) = 120 × 0.8054 ≈ 96.6 kg. Step 3: Load the bar to approximately 96–97 kg for sets of 8. This weight represents roughly 80.5% of your 1RM, squarely within the hypertrophy intensity zone.
Frequently asked questions
What rep range is most effective for muscle hypertrophy?
Research consistently shows that a broad range of rep counts — from as low as 5 to as high as 30 — can stimulate hypertrophy, provided sets are taken close to muscular failure. However, the 6–12 rep range at 65–85% of 1RM remains the most time-efficient hypertrophy stimulus because it balances mechanical tension (heavier loads) with metabolic stress (sufficient time under tension). Very low reps (1–4) primarily develop neural strength adaptations, while very high reps (20+) can build muscle but require proximity to failure that many lifters find uncomfortable. Most evidence-based hypertrophy programs use a mix of rep ranges across different exercises.
How accurate is the Epley formula for estimating working weight from a one-rep max?
The Epley formula and its derivatives are population-average estimates and can deviate from individual reality by 5–10%, especially at the extremes. The formula becomes less accurate above 10 reps because fatigue and endurance factors vary widely between individuals. It is best used as a starting point — load the calculated weight, perform your set, and adjust based on actual performance and proximity to failure. More experienced lifters develop good intuition for their own strength curves and can use the formula as a rough guide rather than a hard prescription.
Why should I calculate working weight from my one-rep max instead of just guessing?
Training at the wrong intensity is one of the most common programming errors — going too light means insufficient stimulus for hypertrophy, while going too heavy compromises form and recovery. Using your 1RM as an anchor gives you an objective, individualized intensity target that scales correctly as you get stronger. When your 1RM increases, your working weights for all rep ranges update automatically, ensuring your program stays optimally challenging. This systematic approach also makes it easier to track progress and compare training cycles over time.