One Rep Max Calculator

Your one-rep max (1RM) is the heaviest weight you can lift for exactly one repetition with proper form. This calculator predicts your 1RM using multiple proven formulas so you can program training percentages without the risk of maxing out in the gym.

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What Is a One-Rep Max?

Your one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with correct technique. It is the gold standard for measuring absolute strength and is the basis for percentage-based training programs used by powerlifters, Olympic weightlifters, and strength athletes worldwide.

Directly testing your 1RM carries inherent injury risk, especially for less experienced lifters. Estimating it from a submaximal set (for example, a weight you can lift for 3-10 reps) provides a safer alternative while still giving you an accurate enough number for training purposes.

Prediction Formulas

Epley Formula

1RM = weight × (1 + reps / 30)

Brzycki Formula

1RM = weight × (36 / (37 − reps))

Lombardi Formula

1RM = weight × reps0.10

All three formulas are most accurate when the rep count is between 2 and 10. Beyond 10 reps, the estimates become less reliable because endurance factors increasingly influence the result.

Using Your 1RM for Programming

% of 1RMReps (approx)Training Goal
90-100%1-2Maximal Strength
80-89%3-5Strength
70-79%6-8Hypertrophy / Strength
60-69%10-15Hypertrophy / Endurance
Below 60%15+Muscular Endurance

Limitations

1RM estimates are exercise-specific and depend on proper form. Fatigue, sleep, nutrition, and psychological readiness all affect your true max on any given day. Use estimated 1RM as a guide for loading, not an absolute ceiling. Re-test every 4-8 weeks to recalibrate your training percentages as strength progresses.

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Frequently Asked Questions

Which 1RM formula is the most accurate?
The Epley and Brzycki formulas are the most commonly validated and tend to produce similar results for rep ranges of 2-10. Neither is definitively superior. This calculator shows results from multiple formulas so you can use the average for greater confidence.
How many reps should I use to estimate my 1RM?
Using a weight you can lift for 3-5 reps provides the most accurate estimate. As rep counts increase beyond 10, the formulas become less reliable because muscular endurance plays a larger role. A heavy set of 5 is a good balance of accuracy and safety.
Should beginners test their one-rep max?
Beginners should generally avoid direct 1RM testing because their technique is still developing, which increases injury risk. Estimating 1RM from a comfortable 8-10 rep set is safer and gives a reliable enough number for programming early-stage training.
How often should I re-test my 1RM?
Re-estimating your 1RM every 4-8 weeks is a common practice. This ensures your training percentages stay aligned with your current strength level. For competitive lifters, a full 1RM test is typically done at the end of a peaking cycle or during a mock meet.
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