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One Rep Max (Brzycki) Calculator

Estimate your 1RM the Brzycki way.

Result

99.31

How it is calculated

The tool estimates the heaviest weight you could lift once from a set of several repetitions with the Brzycki formula: 1RM = w × 36 / (37 − r). Here w is the weight lifted (any unit, the answer comes back in the same unit) and r is the number of repetitions you completed. This is the same as dividing by 1.0278 − 0.0278 × r. One rep returns the weight itself. Reps must be a whole number from 1 to 36 and the weight above zero; a fractional rep count such as 8.5, or anything outside that range, gives no result. The result is rounded to two decimals. It is an estimate: it works best for sets of about 2 to 10 reps taken close to failure, and very high rep counts give inflated numbers.

Worked example

You lift 80 kg for 8 repetitions. Subtract the reps from 37: 37 − 8 = 29. Multiply the weight by 36: 80 × 36 = 2,880. Divide: 2,880 / 29 = 99.31. The calculator shows an estimated one-rep max of 99.31 kg. That is about 124 % of the weight you used for the set.

Try this example →

Common mistakes

  • Entering reps from a set that stopped far short of failure. The formula assumes you could not have done many more reps.
  • Trusting high-rep sets. The tool accepts up to 36 reps, but a set of 30 reps with 80 kg predicts a max of 411.43, which is unrealistic.
  • Entering a fractional rep count, such as 8.5 for a half rep. Only whole reps are accepted and the result is blank otherwise.
  • Mixing pounds and kilograms. The answer is in the unit you typed in.
  • Counting the warm-up weight rather than the working set's weight and reps.

About this calculator

The Brzycki formula — 1RM = weight ÷ (1.0278 − 0.0278 × reps) — estimates the maximum weight you could lift for a single repetition based on a lighter weight lifted for multiple reps, published by strength coach Matt Brzycki in a 1993 issue of the Journal of Physical Education, Recreation and Dance. It assumes a fairly linear relationship between reps performed and percentage of true 1RM, which holds reasonably well in the roughly 2-to-10-rep range but grows less accurate at very high rep counts.

Strength coaches and lifters use rep-max formulas like Brzycki's — alongside competing versions such as the Epley formula — to estimate a 1RM without the injury risk and fatigue cost of actually testing a maximal single lift, which is useful for programming training percentages (like setting a working weight at 75% of estimated 1RM) and tracking strength progress between true max-out sessions.

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