What is BMR?
Basal metabolic rate, or BMR, estimates how much energy your body would use over 24 hours at complete rest. That energy supports essential functions such as breathing, circulation, temperature regulation, and cellular activity.
An online BMR calculator does not directly measure metabolism. It predicts resting energy from age, body size, and the sex coefficient used by the selected equation. Individual results can differ from laboratory measurement.
How does this BMR calculator work?
The calculator converts U.S. customary measurements to kilograms and centimeters when necessary, validates every entry, and applies the equation you select. Results include calories per day, calories per hour, kilojoules per day, a calculated BMI, and activity-level estimates.
Mifflin-St Jeor is the default. The original study developed the equation from measured resting energy expenditure in 498 adults. Revised Harris-Benedict is included as a second established estimate.
BMR formulas used
Mifflin-St Jeor
Female: BMR = 10W + 6.25H − 5A − 161
Revised Harris-Benedict
Female: BMR = 447.593 + 9.247W + 3.098H − 4.330A
In these equations, W is weight in kilograms, H is height in centimeters, and A is age in years. These predictive equations are often described as BMR or resting metabolic rate equations; a controlled laboratory test is needed for a measured value.
How to use the BMR calculator
- Choose U.S. Customary or Metric units.
- Select the sex coefficient used by the equation and enter age.
- Select Mifflin-St Jeor or revised Harris-Benedict.
- Enter current height and weight.
- Select Calculate BMR and review the main estimate and activity comparison.
Select Reset to clear every input and result. You can copy, download, or print a completed result.
How should you interpret a BMR result?
The main number is an estimated amount of energy in calories per day at rest. It is not a minimum that every person must eat, and it is not automatically a weight-loss or maintenance target.
The activity comparison multiplies BMR by commonly used activity factors. For a dedicated maintenance-energy estimate, use the TDEE calculator. These broad categories are planning estimates; occupation, step count, exercise intensity, body composition, health status, and measurement error can all change actual energy use.
Limitations and appropriate use
Predictive equations can overestimate or underestimate an individual's measured resting energy expenditure. They are less suitable for pregnancy or breastfeeding, children, people with significant medical conditions, hospitalized patients, and situations requiring clinical nutrition support.
For an individualized assessment, a registered dietitian or qualified health professional can consider medical history, body composition, weight trends, and measured energy expenditure where appropriate.
Frequently asked questions about BMR
Sources and methodology
The equations and context on this page are documented with primary research and U.S. government resources.