Basal Metabolic Rate Calculator
Estimate how many calories your body burns each day at complete rest with the Mifflin-St Jeor equation, in metric or imperial units.
Calculation Examples
How to Use the Basal Metabolic Rate Calculator
Enter your age, sex, weight and height, pick metric (kg, cm) or imperial (lb, inches) and click "Calculate". Imperial inputs convert to metric first (1 lb = 0.4536 kg, 1 inch = 2.54 cm). The calculator then applies the Mifflin-St Jeor equation (Mifflin et al., 1990): \[ \text{BMR}_{\text{men}} = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} + 5 \] \[ \text{BMR}_{\text{women}} = 10 \times \text{weight (kg)} + 6.25 \times \text{height (cm)} - 5 \times \text{age (years)} - 161 \] The result is the energy, in kilocalories per day, that your body uses at complete rest. It leaves out all physical activity.
For a 30-year-old man who weighs 80 kg and is 180 cm tall: \(10 \times 80 + 6.25 \times 180 - 5 \times 30 + 5 = 1{,}780\) kcal/day. To get your total daily energy expenditure (TDEE), multiply BMR by an activity factor from 1.2 to 1.9: \(1{,}780 \times 1.55 \approx 2{,}759\) kcal/day for moderate activity. These are estimates for healthy adults, not medical advice.
Factors That Influence BMR
Lean body mass explains much of the difference in BMR between people of the same weight. Elia (1992) estimated resting energy use at about 13 kcal/kg/day for skeletal muscle and about 4.5 kcal/kg/day for fat tissue. By these figures, 5 kg of extra muscle adds about 65 kcal/day at rest (\(5 \times 13\)), while 5 kg of fat adds about 22 kcal/day (\(5 \times 4.5\)). The effect is real but modest. The brain, liver, heart and kidneys make up a small share of body weight, yet they burn energy at far higher rates per kilogram than muscle.
BMR falls with age, mostly because muscle mass declines (sarcopenia). The Mifflin-St Jeor equation builds this in as 5 kcal/day per year: a man who is 175 cm and 85 kg has a BMR of 1,799 kcal/day at 30 and 1,699 kcal/day at 50. Doherty (2003) reviews how muscle mass and strength decline with age, and regular resistance training is the main strategy shown to slow that loss. Prolonged severe calorie restriction can also push BMR below the predicted value (adaptive thermogenesis), as can clinically diagnosed hypothyroidism.
Useful Tips 💡
- Do not use BMR as a diet target. It leaves out movement, so eating at BMR creates a large deficit for most people. A man with a BMR of 1,780 kcal/day and a TDEE of 2,759 kcal/day would run a deficit of about 980 kcal/day.
- For weight loss, start from TDEE, not BMR. The 2013 AHA/ACC/TOS guideline suggests a deficit of 500 to 750 kcal/day below TDEE, which for 2,759 kcal/day means 2,009 to 2,259 kcal/day.
- Treat the result as an estimate. In a systematic review of 4 equations (Frankenfield et al., 2005), Mifflin-St Jeor landed within 10% of measured resting metabolic rate in more people than the others, but not in everyone. Only indirect calorimetry measures BMR directly.
📋Steps to Calculate
-
Enter your age (years), sex, weight (kg or lb) and height (cm or inches).
-
Select your preferred unit system: metric (kg/cm) or imperial (lb/inches).
-
Click "Calculate" to view your BMR in kilocalories per day using the Mifflin-St Jeor equation.
Mistakes to Avoid ⚠️
- Confusing BMR with TDEE. BMR is the energy at complete rest, and TDEE adds activity and digestion. Using BMR as a daily target underestimates real needs by several hundred kcal/day.
- Choosing Harris-Benedict (1919) out of habit. The Frankenfield et al. systematic review (J Am Diet Assoc, 2005) found Mifflin-St Jeor within 10% of measured resting rate in more nonobese and obese adults than Harris-Benedict, Owen or the WHO/FAO/UNU equation.
- Skipping the recalculation after weight changes. A BMR calculated at 90 kg is about 100 kcal/day too high once you reach 80 kg.
- Using Mifflin-St Jeor unchanged for very muscular athletes. If you know your body fat percentage, Katch-McArdle works from lean body mass: BMR = 370 + 21.6 × lean mass (kg). At 85 kg and 12% body fat, lean mass is 74.8 kg and BMR is 1,986 kcal/day, versus 1,830 kcal/day from Mifflin-St Jeor for a 30-year-old man who is 180 cm tall.
Practical Applications📊
Set a calorie floor. Eating below BMR for long periods without medical supervision risks muscle loss and nutrient gaps. For a 30-year-old woman who is 165 cm and 60 kg (BMR 1,320 kcal/day), a 1,200 kcal/day diet already sits below BMR. The 2013 AHA/ACC/TOS obesity guideline lists 1,200 to 1,500 kcal/day for women and 1,500 to 1,800 kcal/day for men as typical calorie-restricted diets.
Build your TDEE from BMR. Multiply by 1.2 (sedentary), 1.375 (lightly active), 1.55 (moderately active), 1.725 (very active) or 1.9 (extra active). A man with a BMR of 1,780 kcal/day who trains 3 to 5 days a week lands at about 2,759 kcal/day.
Recalculate when your weight changes. Each kilogram changes Mifflin-St Jeor BMR by 10 kcal/day, so losing 5 kg lowers it by 50 kcal/day, and going from 90 kg to 80 kg lowers it by 100 kcal/day.