One-Rep Max (1RM) Calculator
Please enter valid positive numbers for weight and reps. Reps should be between 1 and 15.
function calculate1RM() {
var weightLifted = parseFloat(document.getElementById('weightLifted').value);
var repsPerformed = parseInt(document.getElementById('repsPerformed').value);
var resultDiv = document.getElementById('result');
var errorDiv = document.getElementById('error-message');
resultDiv.style.display = 'none';
errorDiv.style.display = 'none';
resultDiv.innerHTML = ";
if (isNaN(weightLifted) || weightLifted <= 0 || isNaN(repsPerformed) || repsPerformed 15) {
errorDiv.style.display = 'block';
return;
}
// Brzycki Formula: 1RM = Weight * (36 / (37 – Reps))
// Epley Formula: 1RM = Weight * (1 + (Reps / 30))
// Lander Formula: 1RM = (100 * Weight) / (101.3 – 2.67123 * Reps)
// Lombardi Formula: 1RM = Weight * Reps^0.10
// O'Conner Formula: 1RM = Weight * (1 + 0.025 * Reps)
// Using Brzycki for simplicity and common usage
var estimated1RM = weightLifted * (36 / (37 – repsPerformed));
estimated1RM = Math.round(estimated1RM * 100) / 100; // Round to 2 decimal places
var outputHTML = 'Estimated One-Rep Max (1RM): ' + estimated1RM + ";
outputHTML += 'Estimated Reps at Percentage of 1RM:';
outputHTML += '| % of 1RM | Weight | Estimated Reps |
|---|---|---|
| ' + percent + '% | '; outputHTML += '' + weightAtPercent + ' | '; outputHTML += '' + estimatedReps + ' | '; outputHTML += '
Understanding Your One-Rep Max (1RM)
The One-Rep Max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise. It's a crucial metric for strength training, providing a benchmark for your current strength level and a foundation for designing effective workout programs.
Why is 1RM Important?
- Program Design: Most strength training programs prescribe weights as a percentage of your 1RM (e.g., 3 sets of 5 reps at 80% of 1RM). Knowing your 1RM allows you to accurately calculate these training weights.
- Tracking Progress: Regularly testing or estimating your 1RM helps you track your strength gains over time, motivating you and indicating whether your training is effective.
- Setting Goals: A clear 1RM provides a tangible goal to work towards, whether it's increasing your squat, bench press, or deadlift.
- Injury Prevention: By training with appropriate percentages of your 1RM, you can reduce the risk of injury from lifting excessively heavy weights or using improper form.
How the 1RM Calculator Works
Our calculator uses the popular Brzycki formula to estimate your 1RM: 1RM = Weight × (36 / (37 - Reps)). This formula is widely used and provides a reliable estimate, especially when you perform between 2 and 10 repetitions.
To use the calculator, simply input:
- Weight Lifted: The amount of weight you successfully lifted for a set.
- Reps Performed: The maximum number of repetitions you completed with that weight until failure or near failure.
The calculator will then provide your estimated 1RM and a table showing estimated weights for various percentages of your 1RM, along with typical rep ranges for those percentages. This helps you plan your training sessions effectively.
Limitations and Considerations
- Estimation vs. Actual: This calculator provides an estimation. An actual 1RM test involves lifting the maximum weight for one rep, which carries a higher risk of injury and should only be performed with proper warm-up, spotters, and experience.
- Rep Range Accuracy: Formulas are generally most accurate for reps between 2 and 10. If you input a very high number of reps (e.g., 15+), the estimation may be less precise.
- Exercise Specificity: 1RM varies significantly between exercises. Your squat 1RM will be different from your bench press 1RM.
- Individual Differences: Factors like training experience, muscle fiber type, and recovery can influence your actual 1RM.
Using Your 1RM for Training
Once you have your estimated 1RM, you can structure your workouts:
- Strength Training: Typically involves lifting 80-95% of your 1RM for 1-5 repetitions.
- Hypertrophy (Muscle Growth): Often uses 60-80% of your 1RM for 6-12 repetitions.
- Endurance Training: Usually involves less than 60% of your 1RM for 12+ repetitions.
Always prioritize proper form over lifting heavier weight. Listen to your body and adjust your training as needed.