Brzycki One-Rep Max Calculator
The Brzycki formula estimates your one-rep max (1RM), the most weight you can lift once, from a submaximal set. It divides the weight lifted by a factor based on the number of repetitions, which avoids the injury risk of attempting a true maximum. This tool applies the Brzycki equation and also estimates the load for common rep targets. As with all such formulas, the result is an approximation that varies by person and exercise.
Brzycki formula
Estimated 1RM = weight * 36 / (37 - reps)
For r reps: weight = 1RM * (37 - r) / 36
Weight can be in any consistent unit. The equation is equivalent to weight divided by (1.0278 minus 0.0278 times reps). It assumes the set is taken close to failure and is intended for rep counts below about 37; very high rep counts make the denominator approach zero and the estimate unreliable.
Worked example
For 100 lifted for 5 reps: estimated 1RM = 100 * 36 / (37 - 5) = 3600 / 32 = 112.50. The weight for 10 reps = 112.50 * (37 - 10) / 36 = 112.50 * 27 / 36 = 84.38.
Frequently asked questions
How does Brzycki compare to Epley?
Both estimate 1RM from a submaximal set but use different equations. Brzycki often gives a slightly lower estimate than Epley at higher rep counts. Comparing the two can give a useful range.
Why does the formula break down at high reps?
The denominator is 37 minus reps. As reps approach 37 the denominator approaches zero, making the estimate shoot up unrealistically. The formula is intended for lower rep ranges, typically 10 or fewer for best accuracy.
Is an estimated 1RM safe to program from?
Estimated maxes are useful for setting training percentages without testing a true max. Still, program conservatively and adjust to how the lifts actually feel, since the estimate can be off for any individual.
Does the unit matter?
No. Enter kilograms or pounds; the result is in the same unit. The Brzycki equation is unit-independent.
Sources
- Brzycki M, repetition-based one-rep-max estimation, summarised at the U.S. National Library of Medicine: PubMed.
- U.S. Department of Health and Human Services: Physical Activity Guidelines for Americans.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. Educational training estimate. See our methodology.