BMR Calculator (Basal Metabolic Rate)
Enter your sex, age, height and weight to estimate the energy you use in a day at rest, with the Mifflin–St Jeor equation. You can also choose Harris–Benedict, or Katch–McArdle with your body fat percentage.
- With Harris–Benedict (1918, original)1,442 kcal/day
- Per hour57.1 kcal/hour
How it is calculated
Basal metabolic rate is the energy the body uses in a day at rest; it is the base of your total daily need, with the energy spent on movement added on top. These equations are estimates derived from people whose expenditure was measured by indirect calorimetry. Mifflin and colleagues (1990) derived theirs from 498 healthy normal-weight and obese people aged 19 to 78; in the same study the 1919 Harris–Benedict equations overestimated the measured value by 5% on average. Harris and Benedict tabulated their 1918 equations for ages 21–70, 25–124.9 kg and 151–200 cm. Cunningham’s (1991) lean-mass equation, known as Katch–McArdle, reports that lean mass explains 65–90% of the variation in resting energy expenditure. Strictly, the Mifflin–St Jeor and Cunningham equations estimate resting energy expenditure (REE), while Harris and Benedict measured basal metabolism; the tool uses the common name “basal metabolic rate” for all three.
Mifflin–St Jeor: 10 × weight + 6.25 × height − 5 × age + 5 (men) / − 161 (women)Weight in kg, height in cm, age in years; the result is in kcal/day. Harris–Benedict (1918): men 66.4730 + 13.7516 × weight + 5.0033 × height − 6.7550 × age; women 655.0955 + 9.5634 × weight + 1.8496 × height − 4.6756 × age. Katch–McArdle: 370 + 21.6 × lean mass (kg); lean mass = weight × (1 − body fat ÷ 100).- Choose the equation; Mifflin–St Jeor is the default.
- Multiply weight, height and age by the equation’s coefficients, add them up and add the constant for your sex.
- For Katch–McArdle, work out lean mass first; age and sex do not enter this equation.
- Round to whole calories. The tool warns when your values are outside the range given in the equation’s original paper (Mifflin: the subjects’ ages; Harris–Benedict: the range the equations were tabulated for).
Example
For a 30-year-old woman, 165 cm and 65 kg, Mifflin–St Jeor gives 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 650 + 1,031.25 − 150 − 161 = 1,370.25 ≈ 1,370 kcal/day. Harris–Benedict for the same person: 655.0955 + 621.621 + 305.184 − 140.268 ≈ 1,442 kcal/day.
Frequently asked questions
Which equation should I use?
The default is Mifflin–St Jeor: it was derived from normal-weight and obese adults, and in the study that produced it Harris–Benedict overestimated the measured value by 5%. If your body fat has been measured reliably, you can choose Katch–McArdle, which uses lean mass only.
Why do the equations give different results?
Each was derived from a different group and with different variables. Roza and Shizgal (1984) found that the Harris–Benedict equations estimate a healthy person’s resting expenditure with a precision of about ±14%; read the result as an estimate, not a measurement. An exact value needs a measurement by indirect calorimetry.
How many calories should I eat a day?
BMR is only what you use at rest; your total daily need is higher with movement. For the daily total, use the Daily Calorie Needs calculator. Before setting a weight-loss or weight-gain target, talk to your doctor or a dietitian.
I don’t know my body fat percentage. What should I do?
Mifflin–St Jeor and Harris–Benedict do not need it. You can estimate body fat with the Body Fat calculator, but an estimated body fat carries its own error into the Katch–McArdle result.
Why isn’t the revised 1984 Harris–Benedict equation offered?
Every coefficient on this site is checked against its original publication. Until we have checked Roza and Shizgal’s (1984) revised coefficients against their paper, the tool uses the original equations Harris and Benedict published in 1918.
Source
- Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241–7, abstract (equations, 498 subjects, aged 19–78, Harris–Benedict 5% overestimate)
- Harris JA, Benedict FG. A biometric study of human basal metabolism. PNAS 1918;4(12):370–3, p. 373 (equations for men and women, tabulated ranges)
- Cunningham JJ. Body composition as a determinant of energy expenditure: a synthetic review and a proposed general prediction equation. Am J Clin Nutr 1991;54(6):963–9, abstract (REE = 370 + 21.6 × fat-free mass; 65–90%)
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr 1984;40(1):168–82, abstract (±14% precision)