This is the energy your body needs to maintain basic bodily functions at complete rest.
function toggleUnits() {
var radios = document.getElementsByName('unitSystem');
var imperialDiv = document.getElementById('imperialInputs');
var metricDiv = document.getElementById('metricInputs');
for (var i = 0; i < radios.length; i++) {
if (radios[i].checked) {
if (radios[i].value === 'imperial') {
imperialDiv.style.display = 'block';
metricDiv.style.display = 'none';
} else {
imperialDiv.style.display = 'none';
metricDiv.style.display = 'block';
}
}
}
}
function calculateRMR() {
// Get general inputs
var age = parseFloat(document.getElementById('age').value);
var genderRadios = document.getElementsByName('gender');
var gender = 'male';
for (var i = 0; i < genderRadios.length; i++) {
if (genderRadios[i].checked) {
gender = genderRadios[i].value;
}
}
var formula = document.getElementById('formula').value;
var unitRadios = document.getElementsByName('unitSystem');
var isImperial = true;
for (var j = 0; j < unitRadios.length; j++) {
if (unitRadios[j].checked && unitRadios[j].value === 'metric') {
isImperial = false;
}
}
var weightInKg = 0;
var heightInCm = 0;
// Convert inputs to Metric for calculation
if (isImperial) {
var ft = parseFloat(document.getElementById('heightFt').value);
var inch = parseFloat(document.getElementById('heightIn').value);
var lbs = parseFloat(document.getElementById('weightLbs').value);
if (isNaN(ft)) ft = 0;
if (isNaN(inch)) inch = 0;
// Validation for imperial
if (isNaN(lbs) || (ft === 0 && inch === 0) || isNaN(age)) {
alert("Please enter valid weight, height, and age.");
return;
}
weightInKg = lbs * 0.453592;
heightInCm = ((ft * 12) + inch) * 2.54;
} else {
var cm = parseFloat(document.getElementById('heightCm').value);
var kg = parseFloat(document.getElementById('weightKg').value);
// Validation for metric
if (isNaN(cm) || isNaN(kg) || isNaN(age)) {
alert("Please enter valid weight, height, and age.");
return;
}
weightInKg = kg;
heightInCm = cm;
}
var rmr = 0;
// Calculation Logic
if (formula === 'mifflin') {
// Mifflin-St Jeor Equation
// 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
var base = (10 * weightInKg) + (6.25 * heightInCm) – (5 * age);
if (gender === 'male') {
rmr = base + 5;
} else {
rmr = base – 161;
}
} else {
// Harris-Benedict Equation (Revised)
// Men: 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) – (5.677 × age in years)
// Women: 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) – (4.330 × age in years)
if (gender === 'male') {
rmr = 88.362 + (13.397 * weightInKg) + (4.799 * heightInCm) – (5.677 * age);
} else {
rmr = 447.593 + (9.247 * weightInKg) + (3.098 * heightInCm) – (4.330 * age);
}
}
// Display Result
var resultDiv = document.getElementById('rmr-result-section');
var resultSpan = document.getElementById('rmrValue');
resultSpan.innerText = Math.round(rmr);
resultDiv.style.display = 'block';
// Smooth scroll to result
resultDiv.scrollIntoView({ behavior: 'smooth' });
}
How Is Resting Metabolic Rate Calculated?
Your Resting Metabolic Rate (RMR) represents the number of calories your body burns while at complete rest. Even when you are sleeping or sitting on the couch doing nothing, your body requires energy to maintain essential functions such as breathing, circulating blood, controlling body temperature, and cell growth.
Understanding how RMR is calculated is the first step in creating a tailored nutrition plan, whether your goal is weight loss, muscle gain, or weight maintenance. It serves as the baseline for your Total Daily Energy Expenditure (TDEE).
The Mathematics Behind RMR
While the only way to measure RMR with 100% accuracy is through clinical calorimetry (measuring gas exchange in a lab), mathematicians and scientists have developed formulas that provide highly accurate estimates based on anthropometric data. The calculator above utilizes the two most respected equations in the field.
1. The Mifflin-St Jeor Equation
Published in 1990, this is currently considered the "gold standard" for calculating RMR due to its reliability across various demographics. It is the formula used by the American Dietetic Association.
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
2. The Harris-Benedict Equation
Originally created in 1919 and revised in 1984, this was the standard for decades. While still widely used, studies suggest it may slightly overestimate calorie needs in modern, more sedentary populations compared to Mifflin-St Jeor.
Men: 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) – (5.677 × age in years)
Women: 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) – (4.330 × age in years)
Factors That Influence Your RMR
While the formulas above use weight, height, age, and gender, several biological factors influence your actual metabolic rate:
Factor
Impact on RMR
Muscle Mass
Muscle tissue burns more calories at rest than fat tissue. A higher lean body mass results in a higher RMR.
Age
Metabolism naturally slows down as we age, largely due to a loss of muscle mass and hormonal changes.
Genetics
Some individuals naturally have a faster or slower metabolic rate based on their genetic makeup.
Hormones
Thyroid issues (hypothyroidism or hyperthyroidism) can significantly decrease or increase RMR.
RMR vs. BMR: What's the Difference?
You will often hear Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR) used interchangeably, but there is a subtle technical difference:
BMR (Basal Metabolic Rate): The absolute minimum energy required for survival, measured under very strict laboratory conditions (dark room, immediately upon waking, after 12 hours of fasting).
RMR (Resting Metabolic Rate): The energy required for a body at rest, but measured under less strict conditions (e.g., sitting comfortably during the day). RMR is typically about 10% higher than BMR due to the energy cost of digestion and recent movements.
For practical purposes, such as diet planning, the difference is negligible, and RMR is the more practical metric to use.
How to Use Your RMR Number
Your RMR is not the total number of calories you burn in a day. To find your maintenance calories (Total Daily Energy Expenditure or TDEE), you must multiply your RMR by an activity factor:
Sedentary (desk job, little exercise): RMR × 1.2
Lightly Active (exercise 1–3 days/week): RMR × 1.375
Moderately Active (exercise 3–5 days/week): RMR × 1.55
Very Active (heavy exercise 6–7 days/week): RMR × 1.725
Once you calculate your TDEE, you can subtract 300–500 calories to create a deficit for weight loss, or add calories for muscle gain.