BMR Calculator
This BMR calculator estimates your basal metabolic rate: the energy your body uses at complete rest to breathe, circulate blood and keep organs working. It compares the three best-known equations, Mifflin-St Jeor, the revised Harris-Benedict and, if you know your body fat, Katch-McArdle. You also see the result per hour and in kilojoules, and what it becomes once daily activity is added.
Updated
Results
- Revised Harris-Benedict (kcal/day)For comparison
- Katch-McArdle (kcal/day)Shown only when you enter body fat
- BMR per hour (kcal/h)Mifflin-St Jeor ÷ 24
- BMR in kilojoules (kJ/day)1 kcal = 4.184 kJ
| Activity factor | Calories per day (kcal) |
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Results are estimates. See the methodology below.
How to use the BMR calculator
- Keep US units (pounds, feet and inches) or switch to metric.
- Choose your sex and enter your age (18 or older), weight and height.
- Optional: open Advanced options and enter your body fat percentage. The Katch-McArdle result appears only when you do.
- Read your BMR (Mifflin-St Jeor), the Harris-Benedict comparison, the hourly rate and the value in kJ. The table multiplies your BMR by five activity factors.
BMR formulas used
All formulas use weight in kg and height in cm; US units are converted first.
Mifflin-St Jeor (1990): main result
Men: 10 × weight + 6.25 × height − 5 × age + 5
Women: 10 × weight + 6.25 × height − 5 × age − 161
Harris-Benedict, revised by Roza and Shizgal (1984)
Men: 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
Women: 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age
Katch-McArdle (with body fat)
370 + 21.6 × lean body mass, where lean mass = weight × (1 − body fat %). It ignores age and sex and depends only on lean mass.
Other outputs
Per hour = Mifflin-St Jeor ÷ 24. Kilojoules = kcal × 4.184. The table multiplies BMR by 1.2, 1.375, 1.55, 1.725 and 1.9, the usual factors from sedentary to extremely active.
Examples
Woman, 30, 5 ft 6 in, 140 lb
Mifflin-St Jeor: 1,372 kcal a day, or 57.2 kcal an hour and 5,740 kJ. Harris-Benedict gives 1,424 kcal. With activity factors her daily burn ranges from 1,646 kcal (×1.2) to 2,606 kcal (×1.9).
Man, 50, 6 ft 0 in, 200 lb, 25% body fat
Mifflin-St Jeor: 1,805 kcal (75.2 kcal an hour, 7,553 kJ). Harris-Benedict: 1,898 kcal. Katch-McArdle, from 150 lb of lean mass: 1,840 kcal. The three agree within about 100 kcal.
Woman, 70, 5 ft 3 in, 150 lb
Mifflin-St Jeor: 1,170 kcal; Harris-Benedict: 1,269 kcal. The gap of almost 100 kcal shows that the choice of formula alone moves the estimate by several percent.
What your BMR means
In the lab, BMR is measured lying down and awake, 10 to 12 hours after a meal, after 8 hours of physical rest and no strenuous exercise the day before, in a comfortable room. According to FAO, WHO and UNU, it makes up about 45 to 70% of total daily energy expenditure in adults. Strictly speaking, Mifflin-St Jeor predicts resting energy expenditure, measured under slightly less strict conditions; calculators use both terms for the same idea.
A systematic review of predictive equations found Mifflin-St Jeor the most reliable for healthy adults with and without obesity: it predicted resting metabolic rate within 10% of the measured value more often than the other equations tested. Older adults and ethnic minorities were underrepresented in the studies, and only indirect calorimetry removes the error.
BMR is not your calorie target. You burn more than your BMR every day, so eating at or below it is not a sensible plan without medical supervision. The calculator is for adults; pregnancy, breastfeeding, illness and some medications change energy use.
Frequently asked questions
What is a normal BMR?
There is no single normal value: BMR depends on size, body composition, age and sex. In the examples above it ranges from 1,170 to 1,805 kcal a day. Comparing your result with someone else’s says little.
Which BMR formula is the most accurate?
For most healthy adults, Mifflin-St Jeor, according to the 2005 systematic review. Katch-McArdle can suit very lean or muscular people, but only with a reliable body fat figure.
What is the difference between BMR and TDEE?
BMR is energy at rest. TDEE adds movement, exercise and digestion; the table approximates it with activity factors. To plan intake for a weight goal, use a calorie calculator instead.
Why does my BMR go down with age?
In Mifflin-St Jeor each year of age subtracts 5 kcal a day. Katch-McArdle has no age term: if your lean mass stays the same, its estimate does not change.
Can I measure my BMR exactly?
Yes, with indirect calorimetry, which measures oxygen use and carbon dioxide output. Some clinics and sports labs offer it. Smart scales and fitness trackers only estimate it.
Sources
- Mifflin MD, St Jeor ST, et al. — A new predictive equation for resting energy expenditure in healthy individuals (Am J Clin Nutr, 1990)
- Frankenfield D, Roth-Yousey L, Compher C — Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review (J Am Diet Assoc, 2005)
- Roza AM, Shizgal HM — The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass (Am J Clin Nutr, 1984)
- FAO/WHO/UNU — Human energy requirements, chapter 5: Energy requirements of adults
- National Academies Press — Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids
This calculator gives general estimates for adults and is not medical or nutrition advice. For pregnancy, breastfeeding, eating disorders or medical conditions, talk to a doctor or registered dietitian.