Resting Metabolic Rate Calculator

TL;DR: To calculate resting metabolic rate (RMR), use the Mifflin-St Jeor equation: for men, RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5; for women, RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161, with the result expressed in calories per day.

What Is the Resting Metabolic Rate Calculator?

The Resting Metabolic Rate Calculator estimates the number of calories your body burns while at complete rest, typically measured in the morning after an overnight fast and before any physical activity. This value represents the energy required to maintain vital physiological functions—such as breathing, blood circulation, cell production, and nerve conduction—while you are awake but lying still. Unlike Basal Metabolic Rate (BMR), which requires highly controlled laboratory conditions (e.g., having fasted for 12 hours and lying in a thermoneutral environment), RMR is a more practical measurement that is usually slightly lower (by approximately 5–10%) than your actual total daily energy expenditure but still provides a solid foundation for dietary planning.

This calculator is essential for athletes, fitness enthusiasts, nutritionists, and anyone attempting to manage their weight. Knowing your RMR gives you the baseline number you need to determine a calorie deficit for weight loss, a surplus for muscle gain, or a maintenance level for weight stabilization. Without this starting point, you are essentially guessing at your daily energy needs, which often leads to under-eating (slowing metabolism) or over-eating (storing fat). By using the RMR value, you can then multiply it by an activity factor (1.2 for sedentary, 1.375 for light activity, 1.55 for moderate, 1.725 for very active) to estimate total daily calorie needs.

The calculator applies the Mifflin-St Jeor equation, which was developed in 1990 and is currently considered by the Academy of Nutrition and Dietetics to be the most accurate predictive formula for the general population. It has been validated against indirect calorimetry in numerous studies and outperforms older equations like Harris-Benedict or Katch-McArdle for individuals who are not extremely lean athletes. The formula accounts for age, sex, height, and weight, and it is particularly reliable for adults aged 19 to 78 with a Body Mass Index between 18 and 35.

How to Use the Calculator

1. Enter your weight: Input your current body weight in kilograms (kg). If you know your weight in pounds, divide that number by 2.2046 to get kilograms. For example, 165 lbs ÷ 2.2046 = 74.84 kg.
2. Enter your height: Input your height in centimeters (cm). To convert from feet and inches, multiply the total inches by 2.54. For a person who is 5'9" (69 inches total), this equals 69 × 2.54 = 175.26 cm.
3. Enter your age: Type your current age in years. The calculator works for ages 19 to 78, but the formula has been tested most thoroughly on adults over 30.
4. Select your sex: Choose either "Male" or "Female." This selection adjusts the formula by adding +5 for males or subtracting −161 for females to account for differences in lean muscle mass and hormonal profiles.
5. Click "Calculate": The calculator automatically applies the Mifflin-St Jeor equation and instantly displays your RMR in calories per day.

After you receive your result, always cross-check that you entered the correct units. A very common error is accidentally entering pounds as kilograms, which would make your RMR more than double what it should be—for example, entering 75 lbs instead of 75 kg would produce a wildly inaccurate result that could misguide your nutrition plan.

Formula and Calculation Method

The calculator uses the Mifflin-St Jeor equation, which is split into two separate formulas depending on biological sex. The equation takes your weight as a primary driver (since heavier bodies require more energy to maintain), your height (because taller individuals typically have more tissue mass), and your age (since metabolic rate declines roughly 2–3% per decade after age 30 due to loss of lean muscle mass).

For males: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5

For females: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

Let us walk through the exact example from the introduction: a 30-year-old male who weighs 75 kg and is 175 cm tall. Following the male formula:

RMR = (10 × 75) + (6.25 × 175) − (5 × 30) + 5

First, multiply: 10 × 75 = 750; 6.25 × 175 = 1093.75; 5 × 30 = 150. Then add the constants: +5. Now simplify:

750 + 1093.75 = 1843.75; subtract 150 = 1693.75; then add 5 = 1698.75 calories per day.

So this individual's resting metabolic rate is approximately 1,699 kcal/day. This means that if he were to lie in bed all day without eating, his body would burn roughly 1,699 calories just to keep his heart beating, lungs breathing, and cells functioning. To maintain his current weight, he would need to consume approximately 1,699 × 1.55 (if moderately active) = 2,633 calories daily.

For comparison, if this same person were female instead, the final step would subtract 161 instead of adding 5, giving 750 + 1093.75 − 150 − 161 = 1,532.75 kcal/day—a difference of about 166 kcal, which is consistent with typical metabolic differences due to lower average muscle mass.

Practical Examples

Scenario	Sex	Weight	Height	Age	RMR Result	Interpretation
Sedentary office worker	Female	65 kg (143 lbs)	165 cm (5'5")	40	(10×65)+(6.25×165)−(5×40)−161 = 1,370.25 kcal/day	This woman needs ~1,370 kcal just to rest; adding a sedentary activity factor (1.2) gives 1,644 kcal for maintenance.
Athletic male trainer	Male	85 kg (187 lbs)	180 cm (5'11")	25	(10×85)+(6.25×180)−(5×25)+5 = 2,005 kcal/day	His higher muscle mass and height raise his RMR significantly; he typically needs 2,005 × 1.725 (very active) = 3,459 kcal daily.
Older adult reducing weight	Female	80 kg (176 lbs)	160 cm (5'3")	60	(10×80)+(6.25×160)−(5×60)−161 = 1,339 kcal/day	Age-related muscle loss lowers her RMR; she should aim for a modest deficit of 300–500 kcal from her maintenance level of ~1,607 kcal.

Tips for Accurate Results

• Verify weight units rigorously: The most frequent error is entering weight in pounds while the calculator expects kilograms. A 150-lb person who types "150" instead of "68" inflates their RMR by more than 100%. Always divide pounds by 2.2046 first, or use a weight scale that displays kilograms.
• Do not round intermediate values: When calculating manually, keep all decimals until the final step. Rounding 6.25 × 175 to 1,093 (instead of 1,093.75) early in the process causes a small but meaningless drift; however, accumulating multiple rounding errors across several steps can produce a final result that is off by 20–30 calories, which matters when you are planning precise meal macros.
• Take your measurements in the morning: Your weight fluctuates 1–2 kg throughout the day due to water retention, food in your digestive tract, and glycogen storage. Weigh yourself under consistent conditions—ideally fasting, after using the bathroom, before drinking fluids—to get a stable input value for the calculator.
• Consider body composition: The Mifflin-St Jeor equation assumes average muscle mass relative to age and sex. If you are a bodybuilder with very low body fat, or an endurance athlete with high muscle density, your actual RMR may be 5–10% higher than the calculated value. Conversely, individuals with very high body fat (>35%) may find their calculated RMR slightly overestimates reality.
• Do not apply the result blindly to special conditions: This calculator is not suitable for pregnant or lactating women, who have elevated energy requirements (add 300–500 kcal/day respectively). It is also inappropriate for children under 19, severely obese individuals (BMI > 40), or those with hyper/hypothyroidism, since hormonal imbalances alter metabolic rate beyond the formula's predictive range.
• Re-calculate every 4–6 weeks: As you lose or gain weight, your RMR changes—typically decreasing by about 10–15 kcal for every kilogram lost. Re-running the calculator monthly prevents hunger-driven plateaus caused by eating at an outdated calorie level.

Frequently Asked Questions

What is the difference between RMR and BMR?

Basal Metabolic Rate (BMR) is measured under extremely strict conditions: immediately after waking, after a 12-hour fast, lying still in a thermally neutral room, and fully awake but mentally calm. Resting Metabolic Rate (RMR) is a slightly more lenient measurement—it can be taken after a shorter fast (4 hours), at any time of day, and the subject can be sitting or lying. Because of these less strict conditions, RMR is typically 5–15% higher than BMR. The Mifflin-St Jeor equation used here actually predicts RMR more accurately than pure BMR for practical purposes. For weight management, the difference is negligible—both serve as the baseline for calculating total daily energy expenditure using activity multipliers.

How many calories should I eat to lose weight based on my RMR?

First, multiply your calculated RMR by an activity factor: 1.2 if sedentary, 1.375 if lightly active (1–3 days/week), 1.55 if moderately active (3–5 days/week), 1.725 if very active (6–7 intense days/week), or 1.9 if exceptionally active (physical job + daily training). This gives your maintenance calories. To lose weight sustainably at a rate of 0.5–1 kg per week, create a deficit of 500–1000 calories below maintenance through a combination of diet and exercise. However, never eat below your RMR itself—that is the energy needed for survival. For example, if your RMR is 1,500 kcal and your maintenance is 2,200 kcal, aim to consume between 1,500 and 1,700 kcal daily. Eating below your RMR for extended periods triggers metabolic adaptations and muscle loss, making long-term weight management harder.

Why does my RMR seem lower than my friend's even though we are the same age?

Several factors beyond age influence RMR. The most significant variable is lean body mass—muscle tissue burns 6–10 calories per pound at rest, while fat tissue burns only 2–3 calories per pound. If you weigh the same as your friend but have a higher body fat percentage, your RMR will be lower. Height also matters: taller individuals have longer bones and more organ mass, which increases energy requirements. Additionally, genetics can cause up to a 10–15% variation in metabolic rate even among individuals with identical body composition. Finally, your recent dietary history matters—those who have been on a long-term restrictive diet may have downregulated their metabolism by 5–10%, while those who are well-muscled have upregulated theirs. If you are concerned, consider getting a direct measurement via indirect calorimetry (a breath test measuring oxygen consumption and carbon dioxide production), which provides the gold-standard RMR value for your body.