What resting metabolic rate means

Resting metabolic rate, or RMR, is the amount of energy your body uses while you are resting. That energy supports essential processes such as breathing, circulation, temperature regulation and normal organ function.

This calculator estimates RMR rather than measuring it directly. Your actual resting energy expenditure can differ from the estimate because metabolism varies between individuals.

How this RMR calculator works

The calculator uses the Mifflin St Jeor predictive equation. It uses body weight, height, age and the equation's male or female category to estimate resting energy expenditure in kilocalories per day.

The original Mifflin study developed the equation from measurements in 498 healthy adults, including both normal weight and obese participants. Resting energy expenditure in the study was measured using indirect calorimetry.

RMR formula used

In plain English, the equation combines your weight and height, subtracts an age adjustment and then applies the sex specific constant used by the original equation.

Worked example

Suppose a 35 year old man weighs 80 kg and is 180 cm tall. The calculation is:

His estimated resting metabolic rate would therefore be about 1,757 kilocalories per day. This figure describes estimated energy expenditure at rest and should not be treated as a daily calorie intake target.

Why your actual RMR may be different

Prediction equations cannot account perfectly for individual differences. Body composition, age, health status, genetics and other physiological factors can influence resting energy expenditure.

Research comparing commonly used equations has found the Mifflin St Jeor equation useful for many adults, but individual prediction errors still occur. Estimates may also be less reliable in populations that differ substantially from those used to develop and validate the equation.

If an accurate measurement is medically important, indirect calorimetry can measure resting energy expenditure from respiratory gas exchange rather than predicting it from body measurements.

Limitations

• This calculator is intended for adults aged 19 or older.
• The original Mifflin study included adults aged 19 to 78.
• The result is a statistical estimate, not a direct measurement of metabolism.
• The equation uses male and female categories because the original model contains different constants for them.
• Pregnancy, serious illness and some medical conditions can change energy requirements in ways this simple equation does not capture.
• The result does not include exercise, ordinary daily activity or the energy used to digest food.

Methodology

Weight entered in pounds is converted to kilograms using 1 pound = 0.45359237 kilograms. Height entered in feet and inches is converted using 1 inch = 2.54 centimeters.

The calculator then applies the Mifflin St Jeor equation and rounds the displayed RMR to the nearest whole kilocalorie per day. The secondary kilojoule figure is calculated using 1 kilocalorie = 4.184 kilojoules.

No activity multiplier is applied because the purpose of this calculator is to estimate resting metabolic rate rather than total daily energy expenditure.

Sources

• Mifflin et al., The American Journal of Clinical Nutrition for the original resting energy expenditure equation.
• Endotext, NCBI Bookshelf for the Mifflin St Jeor RMR equations and units.
• Frankenfield et al. systematic review for evidence comparing commonly used predictive RMR equations.
• Endotext review of human energy expenditure for information on measuring resting energy expenditure using indirect calorimetry.

Methodology last reviewed: September 23, 2026.