How to Calculate Basal Metabolic Rate Formula

Basal Metabolic Rate (BMR) Calculator .bmr-calculator-container { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; max-width: 800px; margin: 0 auto; padding: 20px; background: #f9f9f9; border: 1px solid #e0e0e0; border-radius: 8px; } .bmr-header { text-align: center; margin-bottom: 30px; } .bmr-header h2 { color: #2c3e50; margin-bottom: 10px; } .bmr-form-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; } @media (max-width: 600px) { .bmr-form-grid { grid-template-columns: 1fr; } } .bmr-input-group { margin-bottom: 15px; } .bmr-input-group label { display: block; margin-bottom: 5px; font-weight: 600; color: #555; } .bmr-input-group input[type="number"], .bmr-input-group select { width: 100%; padding: 10px; border: 1px solid #ddd; border-radius: 4px; font-size: 16px; box-sizing: border-box; } .bmr-radio-group { display: flex; gap: 15px; margin-top: 5px; } .bmr-radio-group label { font-weight: normal; cursor: pointer; display: flex; align-items: center; gap: 5px; } .bmr-height-imperial { display: none; /* Hidden by default */ grid-template-columns: 1fr 1fr; gap: 10px; } .bmr-height-imperial input { width: 100%; } .calc-btn { grid-column: 1 / -1; background-color: #3498db; color: white; border: none; padding: 15px; font-size: 18px; border-radius: 4px; cursor: pointer; transition: background-color 0.3s; margin-top: 10px; width: 100%; } .calc-btn:hover { background-color: #2980b9; } .bmr-results { margin-top: 30px; padding: 20px; background-color: #ffffff; border-left: 5px solid #3498db; border-radius: 4px; display: none; /* Hidden until calculated */ } .bmr-result-item { margin-bottom: 15px; border-bottom: 1px solid #eee; padding-bottom: 10px; } .bmr-result-item:last-child { border-bottom: none; } .bmr-result-value { font-size: 24px; font-weight: bold; color: #2c3e50; } .bmr-result-label { font-size: 14px; color: #7f8c8d; text-transform: uppercase; letter-spacing: 1px; } .bmr-article { margin-top: 40px; line-height: 1.6; color: #333; } .bmr-article h3 { color: #2c3e50; margin-top: 25px; } .bmr-article ul { padding-left: 20px; } .bmr-article li { margin-bottom: 8px; } .error-msg { color: #e74c3c; font-size: 14px; display: none; grid-column: 1 / -1; }

BMR & Daily Calorie Calculator

Calculate your Basal Metabolic Rate using the Mifflin-St Jeor Formula

Sedentary (little or no exercise) Lightly active (light exercise 1-3 days/week) Moderately active (moderate exercise 3-5 days/week) Very active (hard exercise 6-7 days/week) Super active (very hard exercise & physical job)
Please fill in all fields with valid numbers.
Basal Metabolic Rate (BMR)
1,650 kcal / day
Calories burned at complete rest
Total Daily Energy Expenditure (TDEE)
2,269 kcal / day
Calories burned based on your activity level

How to Calculate Basal Metabolic Rate Formula

Your Basal Metabolic Rate (BMR) represents the number of calories your body needs to accomplish its most basic (basal) life-sustaining functions. Even when you are resting, your body burns calories by performing basic functions like breathing, circulation, nutrient processing, and cell production.

The Mifflin-St Jeor Equation

This calculator utilizes the Mifflin-St Jeor equation, which is widely considered the standard for reliability in clinical settings. The formula calculates BMR based on four distinct factors: weight, height, age, and gender.

The Formulas:

  • Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
  • Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

Understanding the Input Variables

  • Weight (W): Heavier bodies require more energy to function. Muscle mass is denser than fat and requires more energy to maintain, which is why body composition matters.
  • Height (H): Taller individuals typically have a larger body surface area and more lean mass, resulting in a higher BMR.
  • Age (A): As we age, metabolic rate generally decreases. This is often due to a loss of muscle mass and hormonal changes.
  • Gender: Men generally have a higher BMR than women because they tend to have more lean muscle mass and a lower body fat percentage.

From BMR to TDEE

While BMR tells you what you burn at rest, your Total Daily Energy Expenditure (TDEE) accounts for your physical activity. This is calculated by multiplying your BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (extremely active). To lose weight, you generally aim to consume fewer calories than your TDEE; to gain weight, you consume more.

// Function to toggle between Metric and Imperial input fields function toggleUnits() { var radios = document.getElementsByName('unitSystem'); var selected = 'metric'; for (var i = 0; i < radios.length; i++) { if (radios[i].checked) { selected = radios[i].value; break; } } var weightLabel = document.getElementById('label-weight'); var heightMetric = document.getElementById('height-metric-container'); var heightImperial = document.getElementById('height-imperial-container'); var weightInput = document.getElementById('bmr-weight'); if (selected === 'imperial') { weightLabel.textContent = 'Weight (lbs)'; weightInput.placeholder = 'Ex: 150'; heightMetric.style.display = 'none'; heightImperial.style.display = 'grid'; } else { weightLabel.textContent = 'Weight (kg)'; weightInput.placeholder = 'Ex: 70'; heightMetric.style.display = 'block'; heightImperial.style.display = 'none'; } } function calculateBMR() { // 1. Get Inputs var age = parseFloat(document.getElementById('bmr-age').value); var activityMultiplier = parseFloat(document.getElementById('bmr-activity').value); // Determine Gender var genderRadios = document.getElementsByName('gender'); var gender = 'male'; for (var i = 0; i < genderRadios.length; i++) { if (genderRadios[i].checked) { gender = genderRadios[i].value; break; } } // Determine Unit System var unitRadios = document.getElementsByName('unitSystem'); var unitSystem = 'metric'; for (var j = 0; j < unitRadios.length; j++) { if (unitRadios[j].checked) { unitSystem = unitRadios[j].value; break; } } // 2. Validate and Convert Inputs var weightRaw = parseFloat(document.getElementById('bmr-weight').value); var heightCm = 0; var weightKg = 0; // Validation Check if (isNaN(age) || isNaN(weightRaw)) { document.getElementById('bmr-error').style.display = 'block'; document.getElementById('bmr-result-box').style.display = 'none'; return; } if (unitSystem === 'metric') { var hCmRaw = parseFloat(document.getElementById('bmr-height-cm').value); if (isNaN(hCmRaw)) { document.getElementById('bmr-error').style.display = 'block'; return; } weightKg = weightRaw; heightCm = hCmRaw; } else { // Imperial Conversion var ft = parseFloat(document.getElementById('bmr-height-ft').value); var inch = parseFloat(document.getElementById('bmr-height-in').value); if (isNaN(ft)) ft = 0; if (isNaN(inch)) inch = 0; if (ft === 0 && inch === 0) { document.getElementById('bmr-error').style.display = 'block'; return; } // lbs to kg weightKg = weightRaw / 2.20462; // ft/in to cm var totalInches = (ft * 12) + inch; heightCm = totalInches * 2.54; } // Hide Error if valid document.getElementById('bmr-error').style.display = 'none'; // 3. Apply Mifflin-St Jeor Equation // Men: (10 × weight) + (6.25 × height) – (5 × age) + 5 // Women: (10 × weight) + (6.25 × height) – (5 × age) – 161 var bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age); if (gender === 'male') { bmr += 5; } else { bmr -= 161; } // 4. Calculate TDEE var tdee = bmr * activityMultiplier; // 5. Display Results // Round to integer bmr = Math.round(bmr); tdee = Math.round(tdee); document.getElementById('res-bmr').textContent = bmr.toLocaleString() + " kcal / day"; document.getElementById('res-tdee').textContent = tdee.toLocaleString() + " kcal / day"; document.getElementById('bmr-result-box').style.display = 'block'; }

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