One Rep Max Calculator

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one rep max calculator
Brzycki Formula (Most Popular)Epley FormulaLander FormulaLombardi FormulaO'Conner et al. Formula
Answer:
function calculateResult(){var w=parseFloat(document.getElementById('weight').value);var r=parseFloat(document.getElementById('reps').value);var formula=document.getElementById('given_data').value;var showSteps=document.getElementById('steps').checked;var ansDiv=document.getElementById('answer');if(isNaN(w)||isNaN(r)||w<=0||r<=0){ansDiv.innerHTML='Please enter valid weight and repetitions.';return;}if(r>12){ansDiv.innerHTML='1RM formulas are most accurate for 10 reps or fewer. Results for '+r+' reps may be imprecise.';}var orm=0;var stepsText=";if(formula==='brzycki'){orm=w*(36/(37-r));stepsText='Brzycki Formula: Weight * (36 / (37 – Reps))';}else if(formula==='epley'){orm=w*(1+(r/30));stepsText='Epley Formula: Weight * (1 + (Reps / 30))';}else if(formula==='lander'){orm=(100*w)/(101.3-(2.67123*r));stepsText='Lander Formula: (100 * Weight) / (101.3 – (2.67123 * Reps))';}else if(formula==='lombardi'){orm=w*Math.pow(r,0.1);stepsText='Lombardi Formula: Weight * Reps^0.1′;}else if(formula==='o_conner'){orm=w*(1+(0.025*r));stepsText='O\'Conner Formula: Weight * (1 + (0.025 * Reps))';}var finalResult=orm.toFixed(1);var output='
Estimated 1RM: '+finalResult+'
';if(showSteps){output+='
';output+='Calculation Steps:
Using '+formula.charAt(0).toUpperCase()+formula.slice(1)+' method:
';output+=stepsText+'
';output+='Calculation: '+w+' * (…) = '+finalResult+'
';output+='';output+='';var percents=[100,95,90,85,80,75,70,65,60,50];var repEst=['1′,'2′,'3′,'4′,'6′,'8′,'10','12','15','20'];for(var i=0;i<percents.length;i++){var pWeight=(orm*(percents[i]/100)).toFixed(1);output+='';}output+='
PercentageWeightReps
'+percents[i]+'%'+pWeight+''+repEst[i]+'
';}ansDiv.innerHTML=output;}

How to Use the One Rep Max Calculator

A one rep max calculator is an essential tool for athletes, powerlifters, and fitness enthusiasts who want to measure their maximum strength without the injury risks associated with lifting maximum loads. By entering a weight you can lift for multiple repetitions, this calculator uses scientifically validated formulas to estimate the heaviest weight you could lift for a single, perfect repetition.

To get an accurate result, perform a set of an exercise (like the squat, bench press, or deadlift) until failure. It is recommended to use a weight that you can lift for 3 to 10 repetitions for the highest accuracy.

Weight Lifted
The amount of weight used during your set (include the bar weight).
Repetitions
The total number of complete, successful reps performed with that weight.
Formula Choice
Select between Brzycki, Epley, or Lander based on personal preference or coaching guidelines.

How the One Rep Max is Calculated

The math behind a 1RM calculation involves predicting the point of neuromuscular fatigue. Different researchers have developed slightly different coefficients over the years. The most common formulas are:

Brzycki Formula: 1RM = Weight × (36 / (37 – Reps))

Epley Formula: 1RM = Weight × (1 + (Reps / 30))

Lander Formula: 1RM = (100 × Weight) / (101.3 – 2.67123 × Reps)

  • Weight: The resistance applied.
  • Reps: The count of repetitions performed.
  • 30/36/37: Empirical constants derived from testing thousands of athletes.

One Rep Max Example Calculation

Scenario: A lifter performs the bench press with 225 lbs and manages to complete 5 full repetitions before failing on the 6th.

Step-by-step solution using the Brzycki Formula:

  1. Weight = 225 lbs
  2. Reps = 5
  3. Calculate Denominator: 37 – 5 = 32
  4. Calculate Multiplier: 36 / 32 = 1.125
  5. Final 1RM: 225 × 1.125 = 253.1 lbs

Common Questions

Why should I use a 1RM calculator instead of testing it?

Testing a true 1RM is physically taxing and carries a higher risk of injury, especially for beginners. A one rep max calculator provides a safe estimate that you can use to program your training percentages (e.g., doing sets at 80% of your 1RM) without needing to "max out" every week.

Which formula is the most accurate?

For repetitions under 10, the Brzycki formula is widely considered the most accurate for most people. For higher rep ranges (10+), the Epley formula tends to be slightly more reliable, though all formulas lose accuracy as repetitions increase beyond 12.

Does the calculator work for all exercises?

Yes, it works for multi-joint compound movements like squats, deadlifts, and presses. However, it is less useful for isolation movements like bicep curls or lateral raises, where form breakdown often occurs before true muscular failure.

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