Metabolic Rate Calculator

Q: What is the difference between BMR and RMR?

BMR (basal metabolic rate) is measured under strict lab conditions after a full night of sleep and 12 hours of fasting. RMR (resting metabolic rate) is measured under less strict conditions and is usually a little higher. In everyday use, most people treat the two as roughly the same.

Q: Which activity level should I pick?

Be honest about how much you move. Sedentary means you sit most of the day with little exercise. Lightly active means light exercise 1 to 3 days a week. Moderately active means exercise 4 to 5 days a week. Most people overestimate their activity level, so when in doubt, pick one level lower.

Introduction

Your basal metabolic rate (BMR) is the number of calories your body burns each day just to stay alive. Even when you sleep, your body uses energy to breathe, pump blood, and keep your organs working. Knowing your BMR helps you understand how many calories you need to eat each day to lose weight, gain weight, or stay the same.

This metabolic rate calculator estimates your BMR using three trusted formulas: Mifflin-St Jeor, Revised Harris-Benedict, and Katch-McArdle. Just enter your age, sex, height, and weight. The calculator also shows your total daily energy expenditure (TDEE), which factors in how active you are. You get a step-by-step breakdown of the math, a comparison table for six activity levels, and a chart so you can see your results at a glance.

How to Use Our Metabolic Rate Calculator

Enter a few details about your body below. The calculator will show your basal metabolic rate (BMR), the number of calories your body burns at rest each day. It also shows how many calories you need based on how active you are.

Pick your unit system. Choose US/Imperial for feet and pounds, Metric for centimeters and kilograms, or Other Units for stones and centimeters.

Enter your age. Type your current age in years. The calculator works for ages 15 to 80. The Mifflin-St Jeor equation was derived on adults aged 19 to 78, so results for younger users extrapolate.¹

Select your biological sex. Choose Male or Female. This matters because men and women burn calories at different rates.

Enter your height. If you chose US units, type your height in feet and inches. For Metric or Other Units, type your height in centimeters.

Enter your weight. Type your weight in pounds, kilograms, or stones depending on the unit system you picked.

Enter your body fat percentage (optional). This field only appears if you select the Katch-McArdle formula in Settings. If you know your body fat percentage, type it here for a more accurate result. If you are unsure of your body fat percentage, use our body fat calculator to get an estimate.

Choose your BMR formula in Settings. Mifflin-St Jeor works best for most people. Revised Harris-Benedict is a classic option. Katch-McArdle is best if you are lean or athletic and know your body fat percentage.

Choose your energy unit in Settings. Pick Calories (kcal) or Kilojoules (kJ) to change how your results are displayed.

Click "Calculate" to see your BMR, a full step-by-step breakdown, and a table of daily calorie needs for six activity levels. Click "Reset" at any time to start over with the default values.

What Is Your Basal Metabolic Rate (BMR)?

Your basal metabolic rate, or BMR, is the number of calories your body burns each day just to stay alive. Even when you sleep, your body uses energy to breathe, pump blood, grow cells, and keep your brain working. BMR measures that baseline energy use.

Think of it this way: if you stayed in bed all day and did nothing, your BMR is the fuel your body would still need. For most people it is the largest share of the calories burned in a day.

What Affects Your Metabolic Rate?

Several things change how fast or slow your metabolism runs:

Body size: Bigger bodies need more energy. People who weigh more or are taller tend to have a higher BMR.
Muscle mass: Muscle burns more calories than fat, even at rest. This is why athletes often have a higher metabolic rate.
Age: Metabolism slows down as you get older, partly because muscle mass falls with age.
Biological sex: Males usually have more muscle and less body fat than females, so their BMR tends to be higher.

BMR vs. TDEE: What's the Difference?

BMR only covers the calories you burn at rest. Your total daily energy expenditure (TDEE) adds in all the calories you burn from walking, exercising, and daily tasks. To find your TDEE, you multiply your BMR by an activity factor. This calculator does that math for you across six activity levels, from sedentary to extra active.

Which BMR Formula Should You Use?

This calculator offers three well-known formulas. The Mifflin-St Jeor equation was derived in 1990 from 498 healthy adults aged 19 to 78.¹ A systematic review found it the most reliable of the common equations.⁶ The Revised Harris-Benedict equation is an older formula that is still widely used: Harris and Benedict published the original in 1918.² Roza and Shizgal re-fitted it in 1984.³ The coefficients here are those 1984 values as printed in a 2021 systematic review of prediction equations.⁴ In the Mifflin-St Jeor study the original Harris-Benedict equations overestimated measured resting energy expenditure by 5%.¹ The Katch-McArdle formula is best for people who know their body fat percentage, especially lean or athletic individuals, because it uses lean body mass instead of total weight. Its published form is Cunningham's 1991 equation, 370 + 21.6 × lean body mass in kilograms.⁵ You can also compare your results with our RMR calculator, which estimates your resting metabolic rate using a similar approach.

Why Knowing Your BMR Matters

Knowing your BMR helps you set smart calorie goals. If you want to lose weight, you need to eat fewer calories than your TDEE. If you want to gain weight or build muscle, you need to eat more. Without knowing your BMR, you are just guessing. Once you have your calorie target, use our macro calculator to split those calories into the right amounts of protein, carbs, and fat. This calculator gives you a solid starting point based on proven science.

Formulas used

Mifflin-St Jeor BMR (Male) ¹

\text{BMR} = (10 \times W) + (6.25 \times H) - (5 \times A) + 5

Mifflin-St Jeor BMR (Female) ¹

\text{BMR} = (10 \times W) + (6.25 \times H) - (5 \times A) - 161

Revised Harris-Benedict BMR (Male) ⁴

\text{BMR} = 88.362 + (13.397 \times W) + (4.799 \times H) - (5.677 \times A)

Revised Harris-Benedict BMR (Female) ⁴

\text{BMR} = 447.593 + (9.247 \times W) + (3.098 \times H) - (4.330 \times A)

Katch-McArdle BMR (Cunningham 1991)

\text{BMR} = 370 + 21.6 \times \text{LBM}

Total Daily Energy Expenditure (TDEE)

\text{TDEE} = \text{BMR} \times \text{Activity Multiplier}

Frequently asked questions

What is the difference between BMR and RMR?

BMR (basal metabolic rate) is measured under strict lab conditions after a full night of sleep and 12 hours of fasting. RMR (resting metabolic rate) is measured under less strict conditions and is usually a little higher. In everyday use, most people treat the two as roughly the same.

What does the activity multiplier do?

The activity multiplier takes your BMR and scales it up based on how active you are. A sedentary person multiplies by 1.2, while a very active person multiplies by 1.725. The result is your estimated total daily energy expenditure (TDEE), which is the total calories you burn in a full day.

How do I know my body fat percentage?

Common ways to estimate body fat include skinfold calipers, a DEXA scan, bioelectrical impedance scales, or the US Navy tape measure method. If you do not know your body fat percentage, use the Mifflin-St Jeor or Harris-Benedict formula instead. Those two do not require body fat.

Why is my BMR lower than my friend's?

BMR depends on your age, sex, height, weight, and muscle mass. A person who is taller, heavier, younger, or more muscular will usually have a higher BMR. Two people of the same age and sex can still have different results because of different body sizes.

Does my BMR change over time?

Yes. Your BMR drops slowly as you age because you tend to lose muscle and gain fat over the years. Losing or gaining weight, building muscle, and hormonal changes can also shift your BMR. It is a good idea to recalculate every few months.

What is the difference between calories and kilojoules?

They are both units of energy. One calorie (kcal) equals 4.184 kilojoules (kJ). The United States and Canada mostly use calories, while Australia and many European countries use kilojoules. This calculator lets you pick whichever unit you prefer.

Will eating below my BMR help me lose weight faster?

Eating below your BMR is not recommended. Your BMR is the minimum energy your body needs for basic functions like breathing and circulation. Eating too far below it can slow your metabolism, cause muscle loss, and harm your health. A safe approach is to eat below your TDEE but above your BMR.

Which activity level should I pick?

Be honest about how much you move. Sedentary means you sit most of the day with little exercise. Lightly active means light exercise 1 to 3 days a week. Moderately active means exercise 4 to 5 days a week. Most people overestimate their activity level, so when in doubt, pick one level lower.

Does exercise increase my BMR?

Exercise does not directly change your BMR, but it helps indirectly. Building muscle through strength training raises your BMR over time because muscle tissue burns more calories at rest than fat tissue does. Cardio burns calories during the workout but has a smaller long-term effect on BMR.

Why are there three different BMR formulas?

Each formula was created at a different time and tested on different groups of people. Mifflin-St Jeor (1990) is the most widely recommended today. A systematic review found it the most reliable of the common equations.⁶ Revised Harris-Benedict (1984) is a well-known classic.³ Katch-McArdle works best for lean or athletic people because it uses lean body mass; the published equation is Cunningham's, from 1991.⁵ Having three options lets you pick the one that fits your body best.

What does 'below average' or 'above average' mean in my results?

The calculator compares your BMR to a typical range for someone of your age, sex, and height with a healthy-weight BMI. Below average means your BMR is lower than most people in that group, often because of lower body weight. Above average means it is higher, often due to higher body weight or more muscle mass. Neither result is automatically good or bad.

Sources

Rate this calculator