One Rep Max Calculator Formula

Understand the math behind the one rep max calculator. Each variable explained with a worked example.

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Formulas Used

Estimated 1RM

one_rm = weight_lifted * (36 / (37 - reps))

90% 1RM (2-3 reps)

ninety_pct = weight_lifted * (36 / (37 - reps)) * 0.9

80% 1RM (7-8 reps)

eighty_pct = weight_lifted * (36 / (37 - reps)) * 0.8

70% 1RM (12-15 reps)

seventy_pct = weight_lifted * (36 / (37 - reps)) * 0.7

Variables

VariableDescriptionDefault
weight_liftedWeight Lifted(lbs)185
repsReps Performed5

How It Works

Brzycki Formula

1RM = Weight x 36 / (37 - Reps)

The Brzycki formula is one of the most widely used 1RM estimation formulas. It is most accurate for sets of 1-10 reps.

Training Load Percentages

% of 1RMRepsTraining Focus 90-100%1-3Strength / Power 80-89%4-6Strength 70-79%8-12Hypertrophy 60-69%12-15Muscular endurance

Worked Example

Bench pressing 185 lbs for 5 reps.

weight_lifted = 185reps = 5
  1. 011RM = 185 x 36 / (37 - 5)
  2. 02= 185 x 36 / 32
  3. 03= 185 x 1.125 = 208.1 lbs
  4. 0490% = 187 lbs, 80% = 166 lbs, 70% = 146 lbs

Frequently Asked Questions

What is a one-rep max?

A one-rep max (1RM) is the maximum weight you can lift for a single repetition with proper form. It is used to program training intensity.

How accurate is the Brzycki formula?

The Brzycki formula is accurate within 5-10% for sets of 1-10 reps. Accuracy decreases for higher rep ranges.

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