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BMR Calculator

Estimate basal metabolic rate from age, sex, height, and weight, with metric or imperial inputs and a visible Mifflin-St Jeor example.

By The Calcumatix Team Reviewed by Calcumatix Editorial Review

Units

Estimated BMR

1,649 cal/day

Estimated calories used each day at rest before activity is added.

Estimate only, not medical or nutritional advice. Add activity with the TDEE calculator.

Quick Answer

BMR is the calories your body burns at rest. This calculator uses the Mifflin-St Jeor equation: for men, 10 times weight in kg plus 6.25 times height in cm minus 5 times age plus 5. A 30-year-old man at 70 kg and 175 cm has a BMR near 1,649 calories per day; women subtract 161 instead of adding 5.

How A BMR Calculator Works, Step By Step

The BMR Calculator estimates basal metabolic rate, the calories your body would use at rest before exercise or daily movement. It uses the Mifflin-St Jeor equation with age, sex, height, and weight. Metric inputs go straight into the formula, and imperial inputs convert pounds to kilograms and inches to centimeters first. BMR is a resting baseline, not a full daily calorie target, because walking, work, training, digestion, and health factors can change total energy use. A 30-year-old male at 70 kg and 175 cm has an estimated BMR of 1,648.75 calories per day, rounded to 1,649. Use the result as a starting estimate for calorie planning, then use a TDEE calculator if you need an activity-adjusted daily estimate. For medical nutrition decisions, compare the number with advice from a qualified clinician or registered dietitian.

BMR Calculator: The Formula Behind The Result

The calculator uses the Mifflin-St Jeor equation. Male metric formula: BMR = 10 x weight kg + 6.25 x height cm - 5 x age + 5. Female metric formula: BMR = 10 x weight kg + 6.25 x height cm - 5 x age - 161.

  • Male metric formula: BMR = 10 x weight kg + 6.25 x height cm - 5 x age + 5.
  • Female metric formula: BMR = 10 x weight kg + 6.25 x height cm - 5 x age - 161.
  • Imperial weight conversion: pounds x 0.45359237 = kilograms.
  • Imperial height conversion: inches x 2.54 = centimeters.
  • Displayed result: calories per day at rest, rounded to the nearest whole calorie.

Mifflin-St Jeor was published as a predictive equation for resting energy expenditure in healthy adults. NCBI Endotext lists Mifflin-St Jeor equations for adult resting metabolic rate.

This result estimates resting energy only. It does not include exercise, job movement, digestion, illness, pregnancy, or personalized nutrition targets.

Using The BMR Calculator: Step By Step

Inputs

  • Units: choose metric for kg and cm, or imperial for lb and inches.
  • Sex: choose the equation constant used by the published formula.
  • Age: enter age in full years.
  • Weight: enter current body weight in the selected unit.
  • Height: enter current height in the selected unit.

Steps

  1. Choose metric or imperial units.
  2. Select the sex used by the formula.
  3. Enter age, weight, and height.
  4. Read the estimated resting calories per day.
  5. Use the TDEE calculator if you need calories with activity included.

BMR Calculator In Practice: A Real Example

Estimate BMR for a 30-year-old male who is 70 kg and 175 cm.

  1. Use the male formula: BMR = 10 x weight kg + 6.25 x height cm - 5 x age + 5.
  2. Substitute the values: BMR = 10 x 70 + 6.25 x 175 - 5 x 30 + 5.
  3. Weight term: 10 x 70 = 700.
  4. Height term: 6.25 x 175 = 1,093.75.
  5. Age term: 5 x 30 = 150.
  6. Combine the values: 700 + 1,093.75 - 150 + 5 = 1,648.75.
  7. Rounding: 1,648.75 rounds to 1,649 calories per day.

The estimated BMR is 1,649 calories per day at rest.

When To Use A BMR Calculator (Or Not)

Use a BMR calculator when you need a resting calorie baseline before adding activity. The number helps frame calorie planning, nutrition conversations, and comparisons with total daily energy expenditure.

BMR is not the same as a full daily calorie need. A person who moves more during the day usually needs more total energy than the resting estimate alone shows.

For nearby tools, use the TDEE calculator to add activity, the BMI calculator for a weight-to-height screening number, or the health calculators hub for related tools.

Assumptions

  • The calculator uses the Mifflin-St Jeor equation.
  • Age is entered in full years.
  • Metric formula inputs use kilograms and centimeters.
  • Imperial inputs are converted to metric before calculation.
  • The result is rounded to the nearest whole calorie.
  • The sex field follows the constants used by the equation.

The result is a resting calorie estimate. It is not a diagnosis, prescription, or personalized meal plan.

Limitations

  • The calculator does not measure metabolism in a lab.
  • The calculator does not use body fat percentage or lean mass.
  • The calculator does not include exercise or daily movement.
  • The calculator is not designed for children, pregnancy, or clinical nutrition decisions.
  • Medical conditions and medications can change energy needs.

In Practice

The most common mistake is eating to your BMR instead of your total daily need. BMR is resting calories only, before any movement, so it is not a target intake. To find calories for the day, multiply BMR by an activity factor to get TDEE. Eating at bare BMR while active usually leaves you under-fuelled.

Related Calculators

TDEE Calculator

Estimate total daily energy expenditure from BMR and activity level, with metric or imperial inputs, formula steps, and a worked example.

Open the Calculator

BMI Calculator

Calculate Body Mass Index from height and weight, and see your World Health Organization weight category.

Open the Calculator

Frequently Asked Questions About BMR Calculator Math

What does a BMR calculator measure?

A BMR calculator estimates calories your body uses at rest before activity is added. The result is a baseline for energy planning, not a full daily calorie target.

How is BMR calculated with Mifflin-St Jeor?

BMR is calculated from weight, height, age, and the sex constant in the Mifflin-St Jeor equation. This calculator converts imperial inputs to metric, applies the formula, and rounds the result to a whole calorie.

Is BMR the same as TDEE?

BMR is not the same as TDEE because BMR excludes activity. TDEE starts with BMR and adds an activity factor, so it is usually higher than resting calories alone.

Why do BMR results differ between calculators?

BMR results differ when calculators use different equations, units, rounding, or activity assumptions. Compare tools by checking whether they use Mifflin-St Jeor, Harris-Benedict, or another method.

Can I use BMR for weight loss planning?

BMR can support weight planning, but it should not be used alone. A practical plan also needs activity, food intake, health context, and professional advice when needed.

How accurate is a BMR calculator?

A BMR calculator gives an estimate, not a lab measurement of metabolism. Body composition, health status, medications, and measurement error can all move real energy needs away from the formula result.

Sources

Reviewed for accuracy against the formula shown above.