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Resting Metabolic Rate (Rmr) Calculator

Calculate your Resting Metabolic Rate (RMR) using the Mifflin-St Jeor or Katch-McArdle equation. Enter age, weight, height, and sex for instant results.

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Resting Metabolic Rate—kcal/day

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What Is Resting Metabolic Rate (RMR)?

Resting Metabolic Rate (RMR) represents the number of calories the body burns while completely at rest to sustain essential physiological functions — breathing, circulation, temperature regulation, and cellular repair. Unlike Basal Metabolic Rate (BMR), which requires strict laboratory fasting and thermoneutral conditions, RMR is measured after only a brief rest period, making it the more practical and widely used metric in clinical nutrition and everyday fitness planning.

RMR typically accounts for 60–75% of total daily energy expenditure (TDEE), making it the single largest driver of daily calorie burn. Accurately estimating RMR provides the essential baseline for designing weight-loss plans, athletic nutrition programs, and clinical feeding protocols.

The Mifflin-St Jeor Equation

The most widely validated predictive formula for RMR is the Mifflin-St Jeor equation, developed in 1990 and endorsed by the Academy of Nutrition and Dietetics as the preferred method for estimating resting energy expenditure in healthy adults. According to a 2023 review published in Nutrients, this equation estimates RMR within ±10% of indirect calorimetry measurements in approximately 80% of healthy non-obese adults — the highest accuracy of any weight-based formula evaluated.

  • Males: RMR = (10 × W) + (6.25 × H) − (5 × A) + 5
  • Females: RMR = (10 × W) + (6.25 × H) − (5 × A) − 161

Where W = body weight in kilograms, H = height in centimeters, and A = age in years.

Variable Breakdown

  • Weight (W): Body mass carries the largest coefficient (×10) because greater tissue volume demands proportionally more energy to maintain cellular homeostasis at rest.
  • Height (H): Taller individuals carry larger organ volume and body surface area, elevating baseline metabolic demand. The coefficient ×6.25 applies when height is expressed in centimeters.
  • Age (A): Metabolic rate declines approximately 1–2% per decade after age 20 as lean muscle mass and hormonal output decrease. The negative coefficient (×−5) captures this physiological trend.
  • Sex constant: The +5 for biological males and −161 for biological females encodes average differences in lean body mass, organ size, and hormonal profiles between the two sexes.

Worked Examples

A 35-year-old male weighing 80 kg and standing 178 cm tall: RMR = (10 × 80) + (6.25 × 178) − (5 × 35) + 5 = 800 + 1,112.5 − 175 + 5 = 1,742.5 kcal/day.

A 35-year-old female weighing 65 kg and standing 163 cm tall: RMR = (10 × 65) + (6.25 × 163) − (5 × 35) − 161 = 650 + 1,018.75 − 175 − 161 = 1,332.75 kcal/day.

The Katch-McArdle Equation

For individuals who know their body fat percentage, the Katch-McArdle equation offers a body-composition-based alternative that eliminates the sex constant by using lean body mass (LBM) directly: RMR = 370 + (21.6 × LBM in kg), where LBM = total body weight × (1 − body fat fraction). A study by Nelson et al. in Medicine and Science in Sports and Exercise confirmed that lean-mass-based equations outperform weight-based formulas in athletic populations where fat-free mass diverges significantly from population averages.

Converting RMR to Total Daily Calorie Needs

Multiply RMR by an activity factor from the USDA Dietary Reference Intake framework to estimate TDEE: sedentary (×1.2), lightly active 1–3 days/week (×1.375), moderately active 3–5 days/week (×1.55), very active 6–7 days/week (×1.725), and extra active with physical labor plus daily training (×1.9). Using the male example above, moderate activity yields TDEE = 1,742.5 × 1.55 = 2,700.9 kcal/day. A 500 kcal/day deficit from this TDEE produces approximately 0.45 kg of weight loss per week.

Accuracy and Clinical Considerations

All predictive equations carry an inherent margin of error. Accuracy decreases in individuals with morbid obesity (BMI > 40), exceptional muscle mass, pregnancy, thyroid disorders, or those on metabolism-affecting medications. For clinical decisions — ICU feeding plans, bariatric surgery support, or oncology nutrition — indirect calorimetry using a metabolic cart remains the gold standard for measuring true resting energy expenditure.

Reference

Frequently asked questions

What is the difference between RMR and BMR?
RMR (Resting Metabolic Rate) and BMR (Basal Metabolic Rate) both measure calories burned at rest, but measurement conditions differ. BMR requires 12+ hours of fasting, full physical rest, and a thermoneutral laboratory environment. RMR requires only 3–4 hours of fasting and light rest, making it more practical. RMR values run roughly 10–20% higher than true BMR. For everyday nutrition and fitness planning, RMR is the more accessible and commonly reported metric.
How accurate is the Mifflin-St Jeor equation for estimating RMR?
The Mifflin-St Jeor equation estimates RMR within ±10% of indirect calorimetry in approximately 80% of healthy, non-obese adults — the highest accuracy among weight-based predictive formulas according to a 2023 review in Nutrients. Accuracy decreases for individuals with a BMI above 40, very high muscle mass (competitive bodybuilders), thyroid disorders such as hypothyroidism, or those taking medications that affect metabolic rate. For high-stakes clinical nutrition decisions, indirect calorimetry remains the gold standard.
When should the Katch-McArdle equation be used instead of Mifflin-St Jeor?
The Katch-McArdle equation — RMR = 370 + (21.6 × lean body mass in kg) — is the better choice when an accurate body fat percentage is available. It is particularly valuable for athletes, bodybuilders, or individuals with unusually high or low body fat, since it targets metabolically active lean tissue directly rather than total body weight. For example, an 80 kg person with 20% body fat has a lean mass of 64 kg, yielding an RMR of approximately 1,752 kcal/day.
How do you calculate total daily calorie needs from an RMR result?
Multiply the RMR result by an activity factor to estimate Total Daily Energy Expenditure (TDEE). Use 1.2 for sedentary desk workers, 1.375 for lightly active individuals exercising 1–3 days per week, 1.55 for moderately active people training 3–5 days per week, 1.725 for very active individuals training 6–7 days per week, and 1.9 for those with physical jobs plus daily training. An RMR of 1,600 kcal/day at moderate activity produces a TDEE of 2,480 kcal/day — the intake needed to maintain current weight.
Does resting metabolic rate decrease with age, and by how much?
Yes. RMR declines approximately 1–2% per decade after age 20, primarily because lean muscle mass decreases at roughly 3–5% per decade — a process called sarcopenia. Since muscle tissue burns approximately 13 kcal/kg/day at rest compared to only 4.5 kcal/kg/day for fat tissue, muscle loss directly lowers RMR. Resistance training two to three times per week and adequate protein intake of 1.2–1.6 g/kg/day are the most evidence-based strategies to slow age-related metabolic decline.
What lifestyle factors can significantly increase resting metabolic rate?
Building lean muscle through progressive resistance training is the most potent long-term strategy, as each additional kilogram of muscle elevates RMR by roughly 13 kcal/day. A high-protein diet (25–30% of calories) raises the thermic effect of food and preserves muscle during caloric restriction. Intense aerobic exercise triggers excess post-exercise oxygen consumption (EPOC), elevating metabolism for up to 24 hours after a session. Consistent sleep of 7–9 hours per night also protects RMR — chronic sleep deprivation suppresses leptin and elevates cortisol, reducing resting metabolic rate by up to 5%.