Strength Calculator

One-Rep Max (1RM) Strength Calculator

Estimate your maximum lifting potential for a single repetition using this calculator. Enter the weight you lifted and the number of repetitions you successfully completed, and we'll provide an estimated One-Rep Max (1RM).

function calculate1RM() { var weightLifted = parseFloat(document.getElementById("weightLifted").value); var repsPerformed = parseInt(document.getElementById("repsPerformed").value); var resultDiv = document.getElementById("result"); if (isNaN(weightLifted) || weightLifted <= 0) { resultDiv.innerHTML = "Please enter a valid positive weight lifted."; return; } if (isNaN(repsPerformed) || repsPerformed 15) { resultDiv.innerHTML = "For best accuracy, use reps between 1 and 15. Calculations with higher reps may be less precise."; } // Using the Brzycki formula: 1RM = Weight / (1.0278 – 0.0278 * Reps) var oneRepMax = weightLifted / (1.0278 – (0.0278 * repsPerformed)); resultDiv.innerHTML = "

Your Estimated One-Rep Max (1RM):

" + "Based on your input, your estimated 1RM is: " + oneRepMax.toFixed(2) + " units." + "*The unit (kg or lbs) will be the same as the 'Weight Lifted' you entered."; } .strength-calculator-container { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; background-color: #f9f9f9; padding: 25px; border-radius: 10px; box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1); max-width: 600px; margin: 30px auto; border: 1px solid #e0e0e0; } .strength-calculator-container h2 { color: #2c3e50; text-align: center; margin-bottom: 20px; font-size: 1.8em; } .strength-calculator-container p { color: #34495e; line-height: 1.6; margin-bottom: 15px; } .calculator-form .form-group { margin-bottom: 18px; } .calculator-form label { display: block; margin-bottom: 8px; color: #2c3e50; font-weight: bold; font-size: 1.05em; } .calculator-form input[type="number"] { width: calc(100% – 20px); padding: 12px; border: 1px solid #ccc; border-radius: 6px; font-size: 1em; box-sizing: border-box; transition: border-color 0.3s ease; } .calculator-form input[type="number"]:focus { border-color: #3498db; outline: none; box-shadow: 0 0 5px rgba(52, 152, 219, 0.5); } .calculator-form button { display: block; width: 100%; padding: 14px 20px; background-color: #28a745; color: white; border: none; border-radius: 6px; font-size: 1.1em; font-weight: bold; cursor: pointer; transition: background-color 0.3s ease, transform 0.2s ease; margin-top: 25px; } .calculator-form button:hover { background-color: #218838; transform: translateY(-2px); } .calculator-form button:active { transform: translateY(0); } .calculator-result { margin-top: 30px; padding: 20px; background-color: #e8f5e9; border: 1px solid #c8e6c9; border-radius: 8px; text-align: center; font-size: 1.1em; color: #2c3e50; } .calculator-result h3 { color: #1e8449; margin-top: 0; font-size: 1.4em; } .calculator-result p { margin-bottom: 5px; } .calculator-result strong { color: #1e8449; font-size: 1.3em; } .calculator-result .error { color: #dc3545; font-weight: bold; } .calculator-result .warning { color: #ffc107; font-weight: bold; } .calculator-result .note { font-size: 0.9em; color: #555; margin-top: 10px; }

Understanding Your One-Rep Max (1RM)

The One-Rep Max (1RM) is the maximum amount of weight you can lift for a single, complete repetition of a given exercise. It's a crucial metric in strength training for several reasons:

• Program Design: Many strength training programs are structured around percentages of your 1RM. Knowing your 1RM allows you to accurately set your working weights for different rep ranges (e.g., 70% of 1RM for 10 reps, 85% for 5 reps).
• Tracking Progress: An increase in your 1RM over time is a clear indicator of improved strength.
• Safety: While directly testing your 1RM can be risky, especially for beginners or with complex lifts, using a calculator provides a safe estimate without the need to lift maximal weight.
• Goal Setting: It helps in setting realistic and challenging strength goals.

How the 1RM Calculator Works

This calculator uses the Brzycki formula, a widely accepted method for estimating your 1RM based on a sub-maximal lift. The formula is:

1RM = Weight Lifted / (1.0278 - 0.0278 * Reps)

To use the calculator, simply input:

1. Weight Lifted: The amount of weight you successfully lifted for a set.
2. Repetitions Performed: The number of reps you completed with that weight.

For example, if you lifted 100 kg for 5 repetitions, the calculator would estimate your 1RM. The more accurately you perform the sub-maximal set (to near failure, but with good form), the more accurate your 1RM estimate will be.

Realistic Examples:

• Example 1: Bench Press
  You bench pressed 80 kg for 8 repetitions.
  Calculation: 80 / (1.0278 – 0.0278 * 8) = 80 / (1.0278 – 0.2224) = 80 / 0.8054 ≈ 99.33 kg.
  Estimated 1RM: Approximately 99.33 kg.
• Example 2: Squat
  You squatted 140 lbs for 3 repetitions.
  Calculation: 140 / (1.0278 – 0.0278 * 3) = 140 / (1.0278 – 0.0834) = 140 / 0.9444 ≈ 148.24 lbs.
  Estimated 1RM: Approximately 148.24 lbs.
• Example 3: Deadlift
  You deadlifted 200 kg for 1 repetition (this is your actual 1RM, but the formula still works).
  Calculation: 200 / (1.0278 – 0.0278 * 1) = 200 / (1.0278 – 0.0278) = 200 / 1 = 200 kg.
  Estimated 1RM: 200 kg.

Important Considerations:

• Accuracy: 1RM calculators provide an estimate. The accuracy can vary based on the individual, the exercise, and the number of reps performed. Generally, using 2-10 reps yields the most accurate results. Very high reps (e.g., 15+) tend to be less accurate.
• Exercise Specificity: Your 1RM will differ significantly between exercises (e.g., bench press vs. squat vs. deadlift).
• Form: Always prioritize proper lifting form. An estimated 1RM assumes good technique throughout the set.
• Fatigue: Factors like fatigue, nutrition, and sleep can influence your performance and thus the accuracy of the estimate.

Use this calculator as a valuable tool to guide your training, but always listen to your body and consult with a fitness professional for personalized advice.