Basal Metabolic Rate

What This Calculator Measures

Estimates basal metabolic rate (BMR) — the energy expended at complete rest — using the Mifflin-St Jeor equation with sex, age, weight, and height.

How to Use

1. Select sex and enter age, weight (kg), and height (cm).
2. The calculator applies the Mifflin-St Jeor equation directly and returns an estimate in kcal/day.
3. Remember that the result is an estimate of resting energy expenditure, not a direct metabolic measurement.
4. To estimate total daily energy expenditure, an activity factor must be applied separately; the calculator does not do this.

Interpretation Guide

The result is an estimate of the energy required at rest; typical adult estimates are roughly 1,600–2,000 kcal/day in men and 1,400–1,800 kcal/day in women, though values vary with age, body size, and body composition. Because there is no single 'normal' BMR, the calculator reports all valid results as normal. BMR is distinct from total daily energy expenditure, which also includes physical activity and the thermic effect of food.

Clinical Significance

Estimating BMR provides a foundation for nutritional assessment and energy-requirement planning in patients in whom resting energy expenditure cannot be measured directly.

When to Use

• Estimating resting energy expenditure when indirect calorimetry is unavailable
• As a component of estimating total daily energy requirements in nutritional assessment
• Educational review of energy balance and resting metabolism

When Not to Use

• As a direct measurement of metabolic rate
• In critically ill patients where measured energy expenditure (indirect calorimetry) is preferred
• In children and adolescents, where pediatric-specific equations may be more appropriate

Limitations

• The Mifflin-St Jeor equation provides an estimate, and individual variation in metabolic rate can be substantial.
• It does not account for body composition, muscle mass, or metabolic stress such as illness, fever, or critical illness.
• BMR is not total energy expenditure; activity and the thermic effect of food must be added separately.
• The estimate assumes weight in kg and height in cm, matching the calculator inputs.

Worked Example

A 40-year-old man weighing 70 kg with a height of 175 cm.

BMR = 10 × 70 + 6.25 × 175 − 5 × 40 + 5 ≈ 1598.8 kcal/day.

Evidence

Source

Nutrition / Endocrinology

Reference

Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

1. Mifflin MD, et al. Am J Clin Nutr. 1990;51(2):241-247.

References

1. Mifflin MD, et al. (Original equation)
2. Academy of Nutrition and Dietetics (Professional organization)