BMR calculator
Enter your sex, age, weight and height. You get an estimate of the calories your body uses at rest, in kcal and kJ.
Free · no signup Runs in your browser
How do I calculate my BMR?
The Mifflin–St Jeor equation, published in 1990, estimates resting energy use in kcal a day from weight in kilograms, height in centimetres and age in years: 10 × weight + 6.25 × height − 5 × age, then add 5 for men or subtract 161 for women. A man of 30 who weighs 80 kg and is 180 cm tall gets 800 + 1,125 − 150 + 5 = 1,780 kcal. A woman of 30 who weighs 65 kg and is 165 cm tall gets 650 + 1,031 − 150 − 161 = 1,370 kcal. It is an estimate for adults, not a measurement.
Why we built this calculator
Basal metabolic rate (BMR) is the starting number behind most questions about energy: how much a person needs to eat, how a diet plan was worked out, how a fitness tracker gets its figures. Many online calculators give it without saying which formula they used or how far to trust it. This one uses one well-known published equation, shows the working so you can check it, gives the answer in kcal and kJ, and says plainly what BMR leaves out.
Everything is worked out in your browser. Nothing you enter is sent anywhere.
How it works
BMR is the energy the body uses to stay alive at complete rest: breathing, circulation, keeping warm, cell repair. The Mifflin–St Jeor equation estimates it from three body measurements and one constant for sex: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + s, where s is +5 for men and −161 for women. The weight and height terms go up with body size, the age term goes down as people get older, and the constant reflects the average difference in body composition between the sexes. The result is in kilocalories a day (one kcal is 4.184 kJ). Imperial inputs are converted first: 1 lb = 0.45359237 kg and 1 inch = 2.54 cm. The optional activity factor multiplies the result so you can see a figure that includes your own estimate of movement; this tool does not tell you which factor to use.
How to use it
- Choose metric or imperial units, and your sex as used in the equation.
- Enter your age, weight and height.
- Read the BMR in kcal and kJ, and check the working line.
- If you want to include activity, enter your own factor (1.2 and up are commonly used; leave it at 1 for BMR alone).
- Use the number as a starting point only; a doctor or dietitian can advise on what you need.
Use cases
- Understanding the number behind a calorie plan or a fitness app
- Comparing your own estimate with a tracker's
- Studying nutrition or exercise science
- Seeing how age, weight and height change the estimate
- Converting between kcal and kJ for food labels
- A starting point for a conversation with a dietitian
Problems you may run into
Most questions are about what the number means.
| What you see | Likely cause | What to do |
|---|---|---|
| My result is different from another calculator | Other calculators use other equations (Harris–Benedict, Katch–McArdle) or add activity | Compare the formula named; this one is Mifflin–St Jeor and shows BMR only |
| The number seems low as a daily calorie need | BMR is energy at rest, not total energy used | Total use is higher because of movement and digestion; this tool does not estimate it for you |
| I am under 18, pregnant or have a medical condition | The equation is for healthy adults | Ask a health professional; do not use this for a child or pregnancy |
| 'Enter weight, height and age' | A field is empty or out of range | Enter an age from 15 to 100, and a plausible height and weight |
| Imperial height | Feet and inches are separate boxes | 5 ft 10 in is 5 and 10, not 5.10 |
| Muscular people | The equation does not know body composition | It may underestimate; a measurement in a clinic is more accurate |
How accurate is it
The Mifflin–St Jeor equation is one of the most used estimates of resting energy use in healthy adults, but it remains an estimate. Individuals can differ from it by a few hundred kcal a day, because muscle uses more energy than fat, genes and hormones differ, and age and health matter. Treat the result as a starting point and watch how your own weight and energy change over weeks. For medical or weight-management decisions, speak to a doctor or dietitian.
The formula
How the answer is worked out.
BMR (men) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5BMR (women) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161kJ = kcal × 4.184; per hour = kcal ÷ 24imperial: 1 lb = 0.45359237 kg; 1 in = 2.54 cm
The equation is for adults. Results are rounded to the nearest kcal. The activity factor is entered by you; the tool does not choose one.
Example: a 30-year-old man
80 kg and 180 cm.
- Weight term10 × 80 = 800
- Height term6.25 × 180 = 1,125
- Age term5 × 30 = 150
- Total800 + 1,125 − 150 + 5 = 1,780 kcal
1,780 kcal a day at rest (about 7,448 kJ)
For a 30-year-old woman of 65 kg and 165 cm it is 1,370 kcal.
Terms on this page
- BMR
- Basal metabolic rate: energy used at complete rest.
- kcal
- A food calorie: 4.184 kilojoules.
Common questions
What does BMR mean?
Basal metabolic rate: the energy the body uses at rest.
Which equation does this use?
Mifflin–St Jeor (1990).
Is BMR the number of calories I should eat?
No. It excludes movement and digestion, and what you need depends on your goals and health.
How many kJ is a kcal?
4.184.
Is it accurate?
It is an estimate; people vary by a few hundred kcal.
Is my information stored?
No.
Is anything I enter sent to a server?
No. The calculation happens in your browser and nothing you type leaves your device.
Where these numbers come from
- Wikipedia — Basal metabolic rate The Mifflin–St Jeor equation: 10.0m + 6.25h − 5.0a + 5 for men and − 161 for women.
Last verified 2026-10-26 Rates on this page are checked against the sources above at least once a year, and whenever the governing authority announces a change. Spotted something out of date? Tell us and we will fix it.
Related calculators
BMI calculator
Work out BMI in metric or imperial units, see the Health Canada adult category and the weight range that gives a BMI of 18.5 to 24.9 for your height.
Open toolFasting window
Work out when your eating window opens and closes on any fasting pattern.
Open calculatorCaffeine calculator
Daily intake against Health Canada limits, plus how much is still in you tonight.
Open calculatorUnit converter
Pick a quantity, choose two units and type a value. You also see every other unit of that quantity at once.
Open toolDue date calculator
Estimate a pregnancy due date from the first day of the last period, a conception date or a known due date, with the weeks pregnant today and the 37 to 41 week range.
Open calculatorCorrected age
Adjusted age for a baby born preterm, with the milestone dates that follow from it.
Open calculator🩺 Health and animal calculators
Estimates only. Every tool in this section names its source and tells you when to ask a professional instead.
See all 10 calculators in this section