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BMR Calculator

Female BMR equals 655 plus 9.6 times weight plus 1.8 times height minus 4.7 times age

Solution

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How It Works

BMR (Basal Metabolic Rate) is the energy your body burns at complete rest — the calories required to keep your heart beating, lungs breathing, and core temperature stable when you're awake, lying still, and have not eaten for 12+ hours. The classic Harris-Benedict equations (1919, revised 1984) estimate BMR from weight, height, and age, with separate coefficients for biological sex. Female BMR = 655 + 9.6w + 1.8h − 4.7a; Male BMR = 66 + 13.7w + 5h − 6.8a, where w is weight in kg, h is height in cm, and a is age in years. The output is in kilocalories per day.

Example Problem

A 30-year-old woman is 165 cm tall and weighs 70 kg. What is her basal metabolic rate using the Harris-Benedict equation?

  1. Pick the female equation: BMR = 655 + 9.6w + 1.8h − 4.7a.
  2. Substitute: BMR = 655 + 9.6 × 70 + 1.8 × 165 − 4.7 × 30.
  3. Multiply: 655 + 672 + 297 − 141.
  4. Add and subtract left to right: 655 + 672 = 1327; 1327 + 297 = 1624; 1624 − 141 = 1483.
  5. Result: BMR ≈ 1,483 kcal/day. To estimate daily calorie needs, multiply by an activity factor (sedentary 1.2 → very active 1.9) to get TDEE.

Key Concepts

BMR is distinct from RMR (resting metabolic rate), which is measured under less strict conditions and runs about 10% higher. The Harris-Benedict equation was revised in 1984 (Roza & Shizgal) with slightly different coefficients, and the Mifflin-St Jeor equation (1990) is now considered the most accurate of the prediction equations for the general population — but Harris-Benedict remains widely taught and used. All prediction equations have ±10% error vs. indirect calorimetry; for clinical work, measured RMR is preferred.

Applications

  • Estimating a daily calorie target when paired with an activity factor (TDEE).
  • Bariatric and weight-management programs to set baseline metabolic numbers.
  • Sports nutrition for planning energy intake during training cycles.
  • Clinical nutrition for parenteral feeding calculations.
  • Educational tool for understanding why caloric needs vary by sex, age, and body size.

Common Mistakes

  • Using BMR as a direct daily calorie target. BMR is the resting baseline — actual needs include activity, digestion (thermic effect of food, ~10%), and exercise. Multiply by an activity factor to get TDEE before using for diet planning.
  • Applying the Harris-Benedict equation to children, pregnant women, or people with severe illness. The equations were derived from healthy adults; specialized methods apply to those populations.
  • Assuming the male coefficients work for all 'male assigned at birth' bodies. Hormone therapy, body composition, and individual variability all matter — the equation is an estimate.
  • Confusing BMR with metabolism speed. A higher BMR mostly reflects body size, not how 'fast' your metabolism is.
  • Mixing units — entering height in inches but selecting cm in the dropdown will produce wildly wrong numbers. The calculator converts internally if both selectors are set correctly.

Frequently Asked Questions

How do you calculate BMR?

Use the Harris-Benedict equation: Female BMR = 655 + 9.6w + 1.8h − 4.7a; Male BMR = 66 + 13.7w + 5h − 6.8a, where w is weight in kg, h is height in cm, and a is age in years. Result is in kilocalories per day.

What is the formula for BMR?

The Harris-Benedict (1919) formula is sex-specific. For women: BMR = 655 + 9.6 × weight(kg) + 1.8 × height(cm) − 4.7 × age(years). For men: BMR = 66 + 13.7 × weight(kg) + 5 × height(cm) − 6.8 × age(years).

What's the difference between BMR and RMR?

BMR is measured under strict laboratory conditions (12-hour fast, fully rested, neutral temperature). RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10% higher than BMR. For everyday calorie estimation, the terms are often used interchangeably.

Is Harris-Benedict the most accurate BMR equation?

No — the Mifflin-St Jeor equation (1990) is now considered slightly more accurate for the general population. Harris-Benedict remains widely used and produces results within ±10% of measured RMR for most healthy adults.

Why does BMR decrease with age?

Two reasons: lean muscle mass tends to decline with age (sarcopenia), and metabolic processes in remaining tissue slow modestly. The Harris-Benedict equation captures the age effect with a linear coefficient (−4.7 for women, −6.8 for men), which is a simplification but matches population averages reasonably well.

How do I use BMR to set a calorie target?

BMR is the resting baseline. To get daily calorie needs (TDEE), multiply by an activity factor: sedentary 1.2, lightly active 1.375, moderately active 1.55, very active 1.725, extra active 1.9. To lose weight, eat ~500 kcal below TDEE per day (≈1 lb/week deficit). To gain, add 200–500 kcal above TDEE.

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