Estimate your Basal Metabolic Rate with the Mifflin-St Jeor equation. Defaults to US imperial units for weight (lb) and height (in). Results update instantly as you type.
1,649
BMR (kcal/day)
1,650
Rounded kcal/day
Mifflin-St Jeor
Formula applied
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How the Mifflin-St Jeor Formula Works
Developed in 1990 and validated against indirect calorimetry measurements on 498 healthy subjects, the Mifflin-St Jeor equation is the most widely recommended predictive formula for basal metabolic rate. It estimates the kilocalories your body would burn per day at complete rest — awake, fasted 12 hours, in a thermoneutral environment, with minimal muscular effort.
When you enter pounds and inches, the calculator converts internally to kg and cm (1 lb = 0.453592 kg; 1 in = 2.54 cm) then applies the original Mifflin-St Jeor equation, producing numerically identical results to metric inputs.
Result Interpretation
Your BMR represents the baseline energy required to sustain vital functions — breathing, circulation, organ function, and basic neural activity. In practice, your total daily calorie needs are always higher than BMR because of the thermic effect of food and physical activity. Multiplying BMR by standard activity factors (1.2 to 1.9) gives your Total Daily Energy Expenditure (TDEE). For healthy adults, Mifflin-St Jeor predictions typically fall within ±10% of measured indirect calorimetry values. Results for individuals outside the validation range (extreme ages, body compositions, or metabolic conditions) may have larger errors.
Frequently Asked Questions
Why is Mifflin-St Jeor preferred over Harris-Benedict?
The original Harris-Benedict equation (1918) and its 1984 revision were derived on different populations and have been shown to produce larger systematic biases on contemporary adult groups. The Mifflin-St Jeor equation uses a simpler constrained structure (identical weight/height/age coefficients across genders, differing only by a single intercept constant) and generally produces closer estimates to measured indirect calorimetry across multiple populations.
What is the difference between BMR and RMR?
BMR (basal metabolic rate) is measured under strict conditions: full post-absorptive state (12+ hours fasting), complete rest, thermoneutral environment. RMR (resting metabolic rate) is measured under less strict conditions (typically after a shorter fast and in a reclined but not fully relaxed state). RMR is usually 3–10% higher than BMR for the same individual. Most calculators, including this one, compute the Mifflin-St Jeor equation, which technically estimates resting energy expenditure but is conventionally labeled BMR in nutrition contexts.
Can I use this BMR result to plan weight loss?
BMR alone is insufficient for calorie planning. You need to multiply by an activity factor to get your TDEE, then apply a calorie deficit if weight loss is your goal. Visit our TDEE Calculator to see all five activity factor levels at once.
How does this calculator handle US units?
When you enter pounds and inches, the calculator converts: 1 lb = 0.453592 kg, 1 in = 2.54 cm. These values feed directly into the original Mifflin-St Jeor equation, so the result is identical whether you use imperial or metric inputs. Your unit preference is saved in local storage for future visits.
Disclaimer: This calculator provides educational estimations only. It is not medical advice, diagnosis, or treatment. Always consult a licensed healthcare provider for medical concerns.