How this calculation works
The One-Rep Max (1RM) Strength Calculator estimates the maximum weight you can lift for a single repetition on compound lifts without risking injury from true 1RM testing.
Mathematical formula and logic
Epley Formula: 1RM = Weight × (1 + Reps / 30). Brzycki Formula: 1RM = Weight / (1.0278 - 0.0278 × Reps).
Worked example
Lifting 225 lbs for 5 clean reps yields an estimated 1RM of 225 × (1 + 5/30) = 262.5 lbs (Epley) and 253.1 lbs (Brzycki), averaging approximately 258 lbs.
Calculation assumptions
- Formulas are most accurate for repetition ranges between 1 and 10 reps to muscular failure.
- Strict lifting technique without bouncing or form breakdown.
Frequently asked questions
Which 1RM formula is most accurate?
The Epley and Brzycki formulas are the two most validated equations in sports science. Epley tends to be more accurate for lower reps (3-6 reps), while Brzycki excels in 5-10 rep sets.
Why calculate 1RM instead of testing a true 1RM?
Testing a true 1-rep maximum places extreme stress on joints, tendons, and the central nervous system, carrying a higher risk of injury. Calculating 1RM from a 3-5 rep set provides a safe, reliable benchmark.
What percentage of 1RM should I use for hypertrophy?
For muscle hypertrophy (growth), train in the 70% to 85% 1RM range (typically 6 to 12 repetitions per set).
What percentage of 1RM is best for pure strength?
For maximum neural strength development, train in the 85% to 95% 1RM range (1 to 5 heavy repetitions per set).
Can I use this 1RM calculator for dumbbells?
Yes, enter the combined total weight of both dumbbells (or calculate each arm individually) for dumbbell presses, rows, or lunges.
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