Mifflin-St Jeor Equation: Resting Energy Expenditure and the Original 1990 Paper

The Mifflin-St Jeor equation estimates your resting energy expenditure — the calories your body burns at complete rest — from your weight, height, age and sex. It was published by Mifflin, St Jeor and colleagues in the American Journal of Clinical Nutrition in 1990, and it is the formula clinical dietitians most often treat as the most accurate for healthy adults.

By Ash · Updated 27 July 2026

What is the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation is a formula that estimates your resting energy expenditure (REE) — also called resting metabolic rate — which is the number of calories your body uses to keep you alive at rest: breathing, circulating blood, and running your organs. It was published in 1990 by M.D. Mifflin, S.T. St Jeor and colleagues at the University of Nevada School of Medicine, who derived it from measurements on 498 healthy adults (251 men and 247 women, aged 19 to 78, spanning normal weight to obesity).

That figure is your resting metabolic rate (RMR), also written REE — close to, and slightly above, your strict basal metabolic rate (BMR), which is measured under stricter conditions. The two are used interchangeably, so this and most calculators report the result as your "BMR" (the difference, explained).

What is the Mifflin-St Jeor formula?

The standard form of the Mifflin-St Jeor formula is:

• Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
• Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

The numbers published in the original 1990 paper were slightly more precise — 9.99 for weight and 4.92 for age — but every clinical reference and calculator rounds them to 10 and 5, which makes no meaningful difference to the result. Working in pounds and inches? Convert first — multiply weight in lb by 0.4536 to get kg, and height in inches by 2.54 to get cm — or use the Mifflin-St Jeor calculator, which takes both unit systems directly.

Two worked examples:

• A 30-year-old man weighing 80 kg at 180 cm: (10×80) + (6.25×180) − (5×30) + 5 = 1,780 calories a day.
• A 30-year-old woman weighing 65 kg at 165 cm: (10×65) + (6.25×165) − (5×30) − 161 = 1,370 calories a day.

Mifflin-St Jeor is not the only resting-burn formula — see how it stacks up against the older Harris-Benedict in the formula comparison, or how often the two disagree in our 840-profile study.

The original 1990 paper

The equation was introduced in a paper titled "A new predictive equation for resting energy expenditure in healthy individuals", published in the American Journal of Clinical Nutrition in February 1990 (volume 51, issue 2, pages 241–247). Its PubMed record is PMID 2305711 and its DOI is 10.1093/ajcn/51.2.241.

The authors measured resting energy expenditure directly, by indirect calorimetry, in 498 healthy adults — 251 men and 247 women, aged 19 to 78 (mean 45, SD 14) — of whom 264 were normal-weight and 234 were obese. Multiple-regression analysis of those measurements against weight, height, age and sex produced the equation, which explained about 71% of the variation in measured resting energy expenditure (R² = 0.71).

The equation as it was originally published

The paper's headline result is a single equation carrying sex as a variable, rather than the two sex-specific versions calculators use today:

REE = (9.99 × weight in kg) + (6.25 × height in cm) − (4.92 × age in years) + (166 × sex) − 161, where sex is 1 for males and 0 for females.

The authors then reported the simplified, sex-separated forms shown above, noting that rounding the coefficients and separating by sex did not affect the equation's predictive value. The two forms agree with each other: for men the last two terms give 166 − 161 = +5, and for women they give 0 − 161 = −161.

What else the paper found

• Fat-free mass was the single best predictor of resting energy expenditure on its own (R² = 0.64), as REE = (19.7 × fat-free mass in kg) + 413. Weight alone was also closely correlated (R² = 0.56).
• The 1919 Harris-Benedict equations overestimated measured resting energy expenditure by 5% in this sample (p < 0.01) — see how the two compare.
• Extra body-composition detail did not help. Including relative body weight and body-weight distribution did not significantly improve the equation's predictive value.

Note precisely what was measured: resting energy expenditure by indirect calorimetry, not strict basal metabolic rate, which requires tighter measurement conditions (the difference, explained). For who the researchers were and why the equation carries their names, see about the equation and its researchers.

How accurate is the Mifflin-St Jeor equation?

It is the most accurate of the common resting-metabolism formulas. In a 2005 systematic review published in the Journal of the American Dietetic Association, Frankenfield and colleagues compared the main equations against rates measured by indirect calorimetry, and the Mifflin-St Jeor equation came within 10% of the measured value in more people — both non-obese and obese — than the older Harris-Benedict, Owen and WHO/FAO/UNU equations, with the narrowest range of error. That review is the basis for the Academy of Nutrition and Dietetics (then the American Dietetic Association) recommending it for routine use. It remains an estimate, though: it can still be off by more than 10% for some individuals — more on how accurate it is and when it is least reliable.

What does it not tell you?

The equation estimates calories burned at rest only. It does not include the energy you spend moving, exercising or digesting food. To estimate the calories you actually burn across a full day, your resting figure is multiplied by an activity factor — see how TDEE is calculated and the difference between BMR and TDEE. And it remains an estimate: the original equation explained about 71% of the variation between people, so treat the number as a well-grounded starting point and adjust it against your real-world results over two to three weeks.

Who is it for? The equation was derived from healthy adults aged 19 to 78. It was not built or validated for children and younger teenagers, during pregnancy, or for clinical conditions that change metabolism — for those groups, use guidance from a doctor or dietitian rather than any online calculator.