BMR Formulas Explained

BMR Formulas Overview

Several mathematical formulas have been developed over the past century to estimate Basal Metabolic Rate. Each was created using different research populations and methodologies, leading to slightly different results. This guide explains the three most widely used BMR equations.

Mifflin - St Jeor Formula (1990)

The Mifflin-St Jeor equation was published in 1990 by Mifflin, St Jeor, Hill, Scott, Daugherty, and Koh in The American Journal of Clinical Nutrition. It is widely considered the most accurate formula for estimating resting energy expenditure in healthy adults.

Mifflin-St Jeor Formula

• Men: $BMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) + 5$
• Women: $BMR = (10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) - 161$

Mifflin-St Jeor Example

A 35-year-old male, 80 kg, 175 cm:

When to Use Mifflin-St Jeor

Best for general population use. Research has shown it more accurately predicts resting metabolic rate than Harris-Benedict in both obese and non-obese adults. This is the default formula in most modern BMR calculators.

Harris-Benedict Formula (1919)

The Harris-Benedict equation was the first widely adopted BMR formula, published by James Arthur Harris and Francis Gano Benedict at the Carnegie Institution of Washington. It was derived from studying 239 healthy subjects.

Harris-Benedict Formula

• Men: $BMR = 88.362 + (13.397 \times \text{weight in kg}) + (4.799 \times \text{height in cm}) - (5.677 \times \text{age})$
• Women: $BMR = 447.593 + (9.247 \times \text{weight in kg}) + (3.098 \times \text{height in cm}) - (4.330 \times \text{age})$

Harris-Benedict Example

Same 35-year-old male, 80 kg, 175 cm:

When to Use Harris-Benedict

The original formula is still referenced in many textbooks. It tends to overestimate true metabolic rate by approximately 5-15% compared to measured values, particularly in overweight and obese individuals.

Harris-Benedict Revised Formula (1984)

In 1984, Roza and Shizgal reevaluated the original Harris-Benedict equation using improved data analysis techniques. However, the revised formula coefficients for men remain the same as the original. The key revision was to the female formula.

Revised Harris-Benedict Formula

• Men: $BMR = 88.362 + (13.397 \times \text{weight in kg}) + (4.799 \times \text{height in cm}) - (5.677 \times \text{age})$
• Women: $BMR = 447.593 + (9.247 \times \text{weight in kg}) + (3.098 \times \text{height in cm}) - (4.330 \times \text{age})$"

When to Use Revised Harris-Benedict

The revised formula is an improvement over the original, particularly for women. Use it when you need a more conservative estimate than the original Harris-Benedict provides.

Comparing the Formulas

Using the same example (35-year-old male, 80 kg, 175 cm):

For the same person as female (35, 80 kg, 175 cm):

Which Formula Should You Choose?

• Mifflin-St Jeor (Recommended) — Most accurate for the general population according to multiple validation studies. Use this unless you have a specific reason to choose another.
• Harris-Benedict (1919) — A solid historical formula. Tends to overestimate by 5-15%. Useful if you want a more generous calorie estimate.
• Harris-Benedict (Revised) — Marginal improvement over the original. Note that the male coefficients are identical to the 1919 version.

Accuracy Considerations

All BMR formulas share certain limitations:

1. They don't measure lean body mass — Two people of the same weight, height, age, and sex can have very different body compositions and therefore different actual BMRs.
2. Research populations — Each formula was derived from specific study groups. Performance may vary across different populations, ethnicities, and body types.
3. Individual variation — Even with perfect inputs, BMR estimates can vary by 10-15% from measured values.

For precise BMR measurement, indirect calorimetry in a clinical setting remains the gold standard. For practical purposes, any of these formulas combined with appropriate activity multipliers will provide a reasonable starting point for calorie planning.