One Rep Max Calculator — Estimate Your 1RM

Weight LiftedEnter a valid weight.

Reps CompletedEnter a valid rep count (1-20).

Estimated One-Rep Max

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85% (Strength)

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70% (Hypertrophy)

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How to Use This Tool

Enter the weight you lifted for a set.
Enter the number of reps you completed with good form.
Click Calculate 1RM to see your estimated max, plus common training percentages.

The Epley Formula

1RM = Weight × (1 + Reps ÷ 30)

This formula, developed by Boyd Epley, estimates your theoretical one-rep maximum based on a set performed with more than one repetition — useful for tracking strength progress without needing to actually attempt a maximal single lift, which carries higher injury risk.

Why Estimate Instead of Test Directly?

Testing a true 1RM requires careful warm-up, spotting, and technique, and carries more injury risk than submaximal training. Estimating from a set of 3-8 reps (where this formula is most accurate) gives a useful, lower-risk approximation for programming purposes.

Using Percentages for Training

85-95% of 1RM: Typically used for strength-focused training (low reps, higher intensity)
65-75% of 1RM: Commonly used for hypertrophy (muscle growth) training (moderate reps)
Below 60% of 1RM: Often used for endurance or technique-focused work

Accuracy Note

The Epley formula (and similar formulas like Brzycki) become less accurate at very high rep counts (15+) — for the most reliable estimate, use a set of roughly 3-8 reps performed to or near failure with good form.

Frequently Asked Questions

How accurate is this estimate?

It's reasonably accurate for sets of about 3-8 reps performed near failure with good form. Accuracy decreases at very high rep counts, where fatigue and endurance factors play a larger role than pure strength.

Should I actually attempt my calculated 1RM in the gym?

Not necessarily — the estimate is most useful for programming training percentages. If you do want to test a true 1RM, do so with proper warm-up, technique, and ideally a spotter, since maximal single lifts carry higher injury risk.

This calculator is provided for general informational and estimation purposes only. Results should not be treated as professional financial, tax, legal, medical, or engineering advice. Always verify critical calculations with a qualified professional or official source before making decisions.