Formula & Calculator
Basal Metabolic Rate (Mifflin-St Jeor)
Estimates the calories your body burns at rest just to keep basic functions running.
Interpretation
BMR = 10×mass + 6.25×height − 5×age + s, with s = +5 for men, −161 for women. Estimates resting energy expenditure. Used for weight management and nutrition planning.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| BMR | Basal metabolic rate | kcal/day |
| mass | Body mass | kg |
| height | Height | cm |
| age | Age | years |
| s | Sex constant (+5 men, -161 women) |
What it means
The Mifflin‑St Jeor equation is a widely validated formula for estimating Basal Metabolic Rate (BMR) – the energy expended at rest. It uses weight (kg), height (cm), age (years), and sex. It is the standard in clinical nutrition and weight‑management programs. BMR is the largest component of total daily energy expenditure. Health professionals use it to calculate caloric needs, to design weight loss or gain plans, and to assess metabolic health. It is more accurate than older equations. Understanding this formula is essential for dietitians, fitness professionals, and individuals seeking to manage their weight effectively.
Worked example
Basal Metabolic Rate – Two Detailed Examples
Real‑World| Parameter | Value |
|---|---|
| mass (kg) | 70 |
| height (cm) | 175 |
| age (yr) | 30 |
| sex | M |
| Parameter | Value |
|---|---|
| mass | 60 |
| height | 165 |
| age | 28 |
| sex | F |
Common mistakes
- Units: mass in kg, height in cm, age in years – use these units exactly.
- Sex coefficient s: +5 for males, −161 for females – do not use the wrong sign.
- BMR: Basal metabolic rate – calories burned at rest.
- Estimates: This is an estimate – individual variations exist (e.g., muscle mass, genetics).
- Use with TDEE: Multiply by activity factor to get total daily energy expenditure.
Applications
The Mifflin‑St Jeor equation is one of the most accurate formulas for estimating basal metabolic rate (BMR) – the number of calories your body needs at rest. It uses weight (kg), height (cm), age (years), and sex (with a different constant for men and women). Nutritionists, dietitians, and fitness professionals use this equation to determine daily calorie needs, to design weight loss or gain plans, and to assess metabolic health. By calculating BMR, individuals can set realistic energy intake targets and understand the foundation of their energy balance. This formula is also used in clinical settings for patients requiring nutritional support. Understanding BMR is essential for managing body weight and overall health.
- Weight management and personalised nutrition planning
- Clinical nutrition and dietetic assessment
- Fitness coaching and sports nutrition
- Research on metabolism and energy expenditure
- Health promotion and lifestyle interventions
Frequently Asked Questions
It estimates the calories your body burns at rest (basal metabolic rate) to keep basic functions running. The formula is:
BMR = 10×mass(kg) + 6.25×height(cm) − 5×age(y) + s, where s = +5 for men, −161 for women.
mass = body weight (kg)
height = stature (cm)
age = years
s = adjustment constant: +5 for men, −161 for women
It is more accurate for modern populations than the Harris‑Benedict equation because it was developed using indirect calorimetry on a diverse sample.
The result is in kilocalories per day (kcal/day).
Measure weight, height, and age; then choose the correct sex constant. For example, a 30‑year‑old man weighing 80 kg and 180 cm tall: BMR = 10×80 + 6.25×180 − 5×30 + 5 = 800 + 1125 − 150 + 5 = 1780 kcal/day.
BMR is measured under strict conditions (fasting, resting, thermoneutral). RMR (resting metabolic rate) is less strict but similar; the Mifflin‑St Jeor formula estimates BMR.
BMR decreases with age because muscle mass tends to decline, reducing the metabolic rate.
- Applying the men's constant to women (or vice versa) – the constant differs by 166.
- Using pounds or inches without converting to kg and cm.
- Treating the result as exact; BMR varies between individuals.
It may underestimate BMR in very muscular people because it does not account for body composition. A formula that includes lean body mass would be more accurate.
BMR typically accounts for 60–75% of TDEE. It is the largest component of daily energy expenditure.