What this BMR Calculator does
The BMR Calculator estimates basal metabolic rate, or BMR, in kilocalories per day. It uses the Mifflin–St Jeor equation with your weight, height, age, and a selectable equation constant. BMR is an estimate of the energy the body uses to support basic functions at rest, such as breathing, circulation, and maintaining body temperature.
The result is best understood as a reference estimate under resting conditions. It does not represent all the energy you use in an ordinary day. Walking, work, exercise, digestion, and other activity contribute to total daily energy expenditure. The result is also not a meal plan or an individual calorie prescription. Actual needs vary, and this equation cannot measure your metabolism directly.
This calculator accepts weight in kilograms, height in centimeters, and age in years. Its output is labeled in kcal/day, the common dietary unit often called calories. The equation offers two constants because the published Mifflin–St Jeor equations use different constants for men and women. Those categories are part of the equation's structure and may not capture every individual's physiology. Treat the estimate as a starting point for general understanding.
How to use the BMR Calculator
Enter the requested measurements and choose the equation constant that matches the version you want to calculate. The default selection is the male equation. Select the female equation to apply its corresponding constant. The tool then combines those entries using the displayed formula.
- Weight: enter kilograms. If you have a measurement in pounds, convert it to kilograms before entering it.
- Height: enter centimeters. Convert feet and inches to centimeters first if needed.
- Age: enter whole years.
- Equation constant: choose either the male equation, which adds 5, or the female equation, which subtracts 161.
For example, consider an adult aged 30 years who weighs 70 kg and is 170 cm tall. With the male equation, the calculation is (10 × 70) + (6.25 × 170) − (5 × 30) + 5. That is 700 + 1,062.5 − 150 + 5, giving an estimated BMR of 1,617.5 kcal/day. With the female equation, the same measurements produce 700 + 1,062.5 − 150 − 161, or 1,451.5 kcal/day. The difference comes from the selected equation constant, not a change in the measurements.
Use consistent, recent measurements if you want to compare estimates over time. Rounding the height or weight can change the output slightly. The calculator displays two decimal places for arithmetic consistency, but the underlying estimate is not precise to a hundredth of a calorie.
How the BMR formula works
The calculation follows the Mifflin–St Jeor equation. For the male equation, it is 10 times weight in kilograms, plus 6.25 times height in centimeters, minus 5 times age in years, plus 5. For the female equation, the same three measurement terms are used, followed by subtracting 161 instead of adding 5.
Each measurement contributes a term to the estimate. Weight and height increase the calculated value as their inputs increase, while the age term reduces it as age increases. The constant is selected separately. Because the equation combines inputs with different units and coefficients, it is important to enter kilograms and centimeters as requested. Entering pounds or inches directly would produce a misleading result.
The formula can be written compactly as (10 × weight) + (6.25 × height) − (5 × age) + constant. For a 70 kg, 170 cm, 30-year-old using the male equation, the units work through their respective coefficients to yield kcal/day. This is a model estimate based on population research. It does not account for every relevant characteristic or replace a direct measurement of energy expenditure.
Use cases for the BMR estimate
A BMR estimate can help explain the difference between resting energy use and the energy required across a full day. It may serve as a basic reference when learning about nutrition concepts, discussing general wellness with a qualified professional, or comparing how the equation responds to different input values.
People interested in activity can use the result to understand why a resting estimate does not reflect a day that includes walking, strength training, sports, or physically demanding work. BMR alone does not calculate the energy cost of those activities. Likewise, it does not indicate what someone should eat. Those questions involve context that this tool does not collect, such as activity patterns, health status, goals, and how energy needs change over time.
It can also be useful for an educational exercise. Try changing one input at a time to see how the mathematical estimate responds. For instance, keeping height, age, and equation constant fixed while adjusting weight isolates the effect of the weight term. Such comparisons demonstrate the formula's behavior, though they do not predict an exact physiological change for a particular person.
Other factors to consider when interpreting BMR
Several factors can affect actual resting energy expenditure that are not represented in this calculator. Body composition, health conditions, medications, hormonal changes, recent illness, and measurement conditions can all matter. The equation uses only a small set of inputs, so two people with the same age, height, weight, and selected constant can still have different energy needs.
Conditions also matter when BMR is measured in a clinical or research setting. A calculation from height and weight is not the same as indirect calorimetry, which estimates energy use from oxygen consumption and carbon dioxide production. The calculator should therefore be used as an estimate rather than a diagnosis or measurement.
If you are making decisions about nutrition or activity because of a medical condition, pregnancy, recovery, or a significant change in weight, consider discussing your circumstances with a qualified health professional. A general equation cannot determine an appropriate intake or activity plan for you. Avoid treating a calculated BMR as a minimum eating target or as a guarantee of a particular outcome.
Frequently asked questions
What does BMR mean?
BMR means basal metabolic rate. It describes the estimated energy used to sustain basic functions at rest, expressed here in kilocalories per day. It does not include the full energy used for movement and daily activities.
Is BMR the same as daily calorie needs?
No. BMR is a resting estimate. Daily energy expenditure also includes physical activity and other processes. This calculator does not estimate total daily energy expenditure, and its result should not be treated as a recommended calorie intake.
Why does the calculator ask for an equation constant?
The Mifflin–St Jeor equation has separate published forms with different constants, commonly described as the male and female equations. The select input chooses which constant to use. These categories are simplifications within the equation and may not fully represent an individual's physiology.
How accurate is the result?
It is an estimate from a commonly used equation, not a direct measurement. Individual results can differ from the calculated value because the formula has limited inputs and people vary in body composition and other characteristics. Two decimal places describe the arithmetic output, not certainty.
Can I use the result to set my diet?
The result alone cannot establish a suitable eating plan or calorie target. Nutrition needs depend on personal circumstances that are outside the formula. For tailored guidance, especially where health concerns are involved, consult a qualified health professional.