What Is BMR and How Is Basal Metabolic Rate Calculated?

This calculator labels its result Basal Metabolic Rate (BMR), but implements the Mifflin–St Jeor prediction equation for resting energy expenditure (REE). The result estimates energy expenditure at rest in calories per day. It is not a laboratory measurement, an exact individual metabolic requirement, total daily energy expenditure or a recommended calorie intake.

What Is Basal Metabolic Rate (BMR)?

BMR refers to energy expenditure under basal conditions. Resting energy expenditure is a related measure of energy expenditure at rest. This calculator predicts REE using the Mifflin–St Jeor equation and presents it under the familiar BMR label; it does not measure either value directly.

How the Mifflin–St Jeor Equation Predicts REE

For the male selection: REE = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5. For the female selection: REE = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161. The result is expressed in calories per day.

Example of a BMR Calculation

For example, consider a 30-year-old man who weighs 70 kg and is 175 cm tall. Using the Mifflin-St Jeor equation: REE = (10 × 70) + (6.25 × 175) − (5 × 30) + 5. This produces predicted REE of approximately 1,649 calories per day, displayed under the BMR label. The result represents an estimate of resting energy expenditure rather than the person's total daily calorie requirement.

BMR vs. Total Daily Energy Expenditure

The predicted REE displayed under the BMR label is not total daily energy expenditure. Total daily energy expenditure includes resting energy expenditure, physical activity and the energy used to process food. This calculator does not calculate that total or recommend calorie intake.

Why Age, Height, Weight and Sex Matter

The Mifflin-St Jeor equation uses age, height, weight and sex because these characteristics are associated with differences in estimated resting energy expenditure. Weight and height affect the mathematical calculation, while age and the sex-specific equation affect the resulting estimate.

Metric and Imperial BMR Calculations

The Mifflin-St Jeor equation uses kilograms for weight and centimeters for height. ToolXone's Metric mode accepts kilograms and centimeters directly. Feet / Pounds mode accepts height in feet and inches and weight in pounds, then converts those measurements to the units required by the equation before calculating the estimate. Imperial height is converted from total inches using 2.54 centimeters per inch, and pounds are converted using 0.45359237 kilograms per pound.

How to Use the BMR Calculator

Select your sex and enter your age. Choose Metric to enter height in centimeters and weight in kilograms, or choose Feet / Pounds to enter height in feet and inches and weight in pounds. Select Calculate BMR to receive predicted REE in calories per day, displayed under the BMR label.

What Does a BMR Result Mean?

The BMR-labelled result is predicted resting energy expenditure in calories per day rather than a precise measurement of an individual's metabolism. Two people with similar characteristics can still have different actual energy requirements. Predicted REE can differ from an individual’s measured resting energy expenditure. This result does not calculate total daily energy expenditure, diagnose a condition, determine appropriate calorie intake or prescribe a weight-management plan.

BMR Is an Estimate, Not a Diagnosis

Predictive equations such as Mifflin-St Jeor provide estimates rather than direct laboratory measurements. Actual resting energy expenditure can differ from the calculated value because individual physiology and other factors vary. The result should therefore be used as general informational guidance rather than a diagnosis or personalized medical recommendation.

BMR and Weight Management

BMR can be useful as one component of a broader understanding of energy needs. However, BMR alone does not determine whether a person will gain, maintain or lose weight. Physical activity, food intake, body composition and other factors also influence overall energy balance.

Who Can Use This BMR Calculator?

The software accepts ages 18–120. The original Mifflin study reported 498 healthy participants aged 19–78. Acceptance of an age by the calculator does not establish that the equation was validated for that age or population. This is not a pediatric energy-needs calculator.

Methodology and Reference

The implemented equations are the simplified sex-specific REE equations reported by Mifflin and colleagues. Their study compared predictions with REE measured by indirect calorimetry. Citing the publication identifies the methodology; it does not imply endorsement of ToolXone.

Mifflin et al. (1990) — A new predictive equation for resting energy expenditure in healthy individuals