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One Rep Max Calculator

Your one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition with proper form. Knowing your 1RM is essential for designing effective strength training programs, as most percentage-based programs prescribe loads as a percentage of your 1RM. Rather than testing your true max — which carries injury risk — you can estimate it from a lighter set using well-established formulas.

Quick Answer

Your 1RM is estimated from submaximal lifts. The Epley formula: 1RM = weight × (1 + reps ÷ 30).

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Enter the weight lifted and reps completed to estimate your one rep max.

How the Formula Works

  1. Perform a set of an exercise with a weight you can lift for 2 to 10 reps with good form. Record the weight and the number of reps completed.

    weight = load lifted, reps = repetitions completed

  2. Epley formula: Multiply the weight by one plus the number of reps divided by 30.

    1RM = weight × (1 + reps ÷ 30)

  3. Brzycki formula: Multiply the weight by 36 divided by the quantity 37 minus the number of reps.

    1RM = weight × (36 ÷ (37 − reps))

  4. Lombardi formula: Multiply the weight by the number of reps raised to the power of 0.10.

    1RM = weight × reps^0.10

  5. Average the three estimates for a more reliable prediction, then use the percentage chart to plan your training loads.

    Average 1RM = (Epley + Brzycki + Lombardi) ÷ 3

Limitations

  • Formulas are most accurate when the rep count is between 2 and 10. Accuracy decreases with higher rep sets.
  • These estimates do not account for individual differences in muscle fiber composition, training experience, or technique proficiency.
  • Fatigue, sleep quality, nutrition, and stress levels can significantly affect actual max performance on any given day.
  • The formulas assume reps were performed to or near muscular failure. Stopping well short of failure will underestimate your 1RM.
  • Different exercises may yield different levels of accuracy. Compound lifts (squat, bench, deadlift) tend to be more predictable than isolation exercises.

Frequently Asked Questions

What is a one-rep max (1RM)?
A one-rep max is the heaviest weight you can successfully lift for exactly one repetition with correct form. It is the gold standard for measuring absolute strength in a given exercise and is widely used to prescribe training intensities.
Why should I estimate my 1RM instead of testing it directly?
Testing a true 1RM places significant stress on your muscles, joints, and nervous system, increasing the risk of injury — especially for beginners and intermediate lifters. Estimating from a submaximal set provides a safe, practical alternative that is accurate enough for programming purposes.
Which formula is the most accurate?
No single formula is universally the most accurate. Epley and Brzycki tend to produce similar results for moderate rep ranges (3-10) and are the most widely cited in research. Lombardi may differ slightly. Averaging all three gives a balanced estimate that reduces the bias of any one formula.
How often should I recalculate my 1RM?
It is a good practice to re-estimate your 1RM every 4 to 8 weeks, or whenever you complete a training cycle. As you get stronger, your working weights should increase accordingly to maintain the correct training stimulus.
Can I use this calculator for any exercise?
Yes, the formulas work for any resistance exercise. However, they tend to be most accurate for barbell compound movements like the squat, bench press, deadlift, and overhead press. Machine and isolation exercises may produce less reliable estimates due to mechanical differences.

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