One Rep Max Calculator

Estimate Your 1-Rep Max

Enter the weight and reps from a recent set to estimate your one-rep max and training percentages.

Parameters

Weight Lifted (kg)

Weight Lifted (lbs)

Reps Performed

Estimated 1RM (Epley)

Enter your set to see your estimated 1RM.

Validation Error

Please provide a valid weight and rep count to proceed.

Understanding One-Rep Max Estimation

Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition. Rather than testing it directly — which carries injury risk — these formulas estimate it from a lighter, safer submaximal set.

Why Estimate Instead of Test?

True 1RM testing requires a spotter, proper warm-up, and carries higher injury risk — estimation from a submaximal set is safer for regular programming.

Accuracy Decreases at Higher Reps

These formulas are most accurate for sets of 1-10 reps — estimates from very high-rep sets (15+) become less reliable.

Training Percentages

Many strength programs are written as a percentage of 1RM (e.g., "3x5 @ 80%") — this table converts your estimate into practical training loads.

Exercise-Specific Variance

These formulas were validated primarily on compound barbell lifts — accuracy varies for isolation exercises or machines.

Epley & Brzycki Formulas

Epley (1985)

\[ 1RM = w \times \left(1 + \frac{r}{30}\right) \]

Brzycki (1993)

\[ 1RM = w \times \frac{36}{37 - r} \]

Where w is the weight lifted and r is the number of reps performed. Epley tends to estimate slightly higher at higher rep counts; Brzycki is considered more conservative.

Important Limitations

An estimate, not a measurement: Actual 1RM can vary from the formula estimate based on individual fatigue resistance and technique.
Best with proper form: A submaximal set performed with breakdown in technique will overestimate true strength capacity.
Not a substitute for supervised testing: If you need a verified 1RM (e.g., for competition), work with a qualified coach.

Key Takeaways

Estimation is safer than direct testing. A submaximal set carries far less injury risk than attempting a true 1RM.
Lower reps give more reliable estimates. Sets of 3-8 reps tend to produce the most trustworthy 1RM predictions.
Use the percentage table for programming. Most strength programs are built around percentages of 1RM.
Consult a professional. Estimated 1RM is not a substitute for a supervised max-effort test — work with a certified trainer to attempt true 1RM lifts safely.

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