Resting Metabolic Rate Calculator

The Resting Metabolic Rate (RMR) Calculator estimates the number of calories your body burns each day just to maintain basic functions — breathing, circulation, hormone production, and cellular repair — without any additional activity. RMR accounts for 60–75% of total daily energy expenditure for most people and is the foundation for setting accurate calorie targets for weight loss, maintenance, or muscle gain.

How to Use This Calculator

1. Enter your weight in kilograms or pounds.
2. Enter your height in centimeters or feet and inches.
3. Enter your age and sex.
4. Select your preferred formula — Mifflin-St Jeor (most accurate for general population), Harris-Benedict, or Katch-McArdle (if you know your lean body mass).
5. Click Calculate to see your RMR in kcal/day from each formula.

What This Calculator Measures

This calculator estimates your resting metabolic rate in kilocalories per day.

• RMR: Calories burned at complete rest in a thermoneutral environment, slightly higher than BMR.
• BMR vs RMR: BMR is measured under strict conditions; RMR is a practical estimate for daily use (typically 10% higher than BMR).
• Lean body mass (LBM): The Katch-McArdle formula uses LBM for the most accurate individual estimate.
• Formula comparison: Multiple formulas give a range; the true value likely falls within that range.

Formula or Logic

Mifflin-St Jeor (men): RMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Women: RMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161. Katch-McArdle: RMR = 370 + (21.6 × LBM in kg). Harris-Benedict (revised): Men: 88.36 + (13.4 × kg) + (4.8 × cm) − (5.68 × age); Women: 447.6 + (9.25 × kg) + (3.1 × cm) − (4.33 × age).

Example Calculations

Example 1: 30-year-old woman, 65 kg, 165 cm. Mifflin-St Jeor: (10×65) + (6.25×165) − (5×30) − 161 = 1,420 kcal/day.

Example 2: 40-year-old man, 85 kg, 180 cm. Mifflin-St Jeor: (10×85) + (6.25×180) − (5×40) + 5 = 1,880 kcal/day.

Understanding Your Results

RMR declines with age (approximately 1–2% per decade after 30) and increases with greater muscle mass. Even small increases in lean muscle tissue meaningfully raise RMR. Crash diets can suppress RMR by 15–30% through adaptive thermogenesis.

Common Mistakes to Avoid

• Confusing RMR with TDEE — multiply RMR by your activity factor to get total daily calorie needs.
• Assuming the formula result is exact — all equations have a margin of error of ±5–15%.
• Severely under-eating relative to RMR, which triggers metabolic adaptation and muscle loss.
• Ignoring how body composition changes (muscle gain or loss) affect RMR over time.