How to Estimate One Rep Max: Epley and Brzycki Formulas

 

A one-repetition maximum, or 1RM, is the greatest load someone can lift once for a particular exercise under defined conditions. An estimated 1RM uses a completed set to approximate that number. The estimate can help describe performance, but it is not a measured maximum or an instruction to attempt the predicted load.

The One Rep Max Calculator compares Epley and Brzycki estimates from a lifted weight and 1 to 10 completed repetitions. It works in kilograms or pounds and displays the results in the same unit as the input.

Use the Epley formula

For sets of 2 to 10 repetitions, the Epley estimate is weight x (1 + repetitions / 30). For 80 kg lifted five times, calculate 80 x (1 + 5 / 30) = 93.333333... . The displayed estimate is 93.33 kg.

The formula is a simplified relationship between load and repetition performance. It does not know the exercise, your technique or how much effort remained after the last repetition. Those details affect how useful the result is.

Compare the Brzycki formula

The Brzycki estimate is weight x 36 / (37 - repetitions). For the same 80 kg and five repetitions, calculate 80 x 36 / (37 - 5) = 90 kg.

The formulas differ by approximately 3.33 kg in this example. That difference is not a confidence interval. It does not establish that your actual maximum lies between 90 and 93.33 kg, or that either number is a suitable training load.

Enter a completed set

Leave Weight unit at Kilograms (kg). Enter Lifted weight 80 and Completed repetitions 5, then select Estimate one rep max. Check that the Epley result is 93.33 kg and the Brzycki result is 90 kg.

Use a set you have already completed with appropriate technique. You do not need to attempt a maximum lift to fill in the calculator. The tool does not ask you to reach failure or prescribe a testing session.

Understand the one-repetition case

At one repetition, this calculator returns the entered weight for both results instead of applying an Epley uplift. This is an explicit handling rule. A successful single repetition shows that you lifted that load, but it does not prove the load was your maximum.

The input limit is ten repetitions. Extending an equation to larger repetition counts can give increasingly uncertain estimates, and this tool rejects those inputs rather than displaying an unrestricted extrapolation.

Keep exercise and load conventions consistent

For a barbell lift, include the bar and plates in total external load. For dumbbells, keep your own recording convention consistent about weight per hand or combined weight. Changing conventions between sessions makes the estimates difficult to compare.

Exercise, range of motion and technique also matter. A result from one exercise should not be treated as a predicted maximum for another. Machine-stack labels, resistance bands and assisted repetitions can involve different resistance mechanics.

This calculator does not add body weight for pull-ups or dips or account for assistance. Those situations need additional assumptions. Do not enter an arbitrary combined load and assume the result has been validated for that movement.

Interpret estimates without treating them as prescriptions

Repetition endurance varies between people and exercises. Fatigue, training experience and how close a set was to failure can change the relationship between completed repetitions and maximum strength. A set stopped early may underestimate a maximum.

The estimates do not assess readiness, injury risk or exercise suitability. They do not recommend a progression, training percentage or heavier attempt. A suitable coach can help interpret performance and select loads for your circumstances.

Changing the unit selector reinterprets the entered number rather than converting it automatically. Results round to two decimal places, but those digits do not imply physiological accuracy. Compare consistently recorded sets and treat the outputs as rough estimates.