Mifflin-St Jeor Resting Energy Calculator
Mifflin-St Jeor Resting Energy Calculator
Resting energy expenditure by the equation current guidance prefers in adults who are not critically ill — with the published accuracy that matters more than the number, and the weight-based targets that have largely replaced stress factors.
Mifflin-St Jeor resting energy expenditure
Sex, weight, height, ageMale, 70 kg, 176 cm, 45 years
Formula
Women: RMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) − 161
- what it predicts
- resting metabolic rate in kcal/day — the energy spent at rest, awake, in a thermoneutral room, several hours after a meal. Not a daily requirement and not a target. Activity and the thermic effect of food sit on top of it, and PENG’s Pocket Guide puts activity at no more than 20% above resting in most inpatients
- the 166 kcal/day sex gap
- the paper’s pooled regression carries a sex term of +166 for men, and the two simplified forms differ by exactly 5 − (−161) = 166. The calculator shows the other sex’s answer alongside, because an equation applied with the wrong intercept is wrong by 166 kcal/day and looks entirely plausible
- the derivation cohort
- 498 healthy adults — 251 men and 247 women, aged 19 to 78, 264 of normal weight and 234 obese, R² 0.71. Everyone in it was healthy, which is the population the equation is for
- two published forms
- the paper gives a pooled regression, 9.99 × weight + 6.25 × height − 4.92 × age + 166 × sex − 161, and the rounded sex-separated forms above. This page implements the rounded forms, which is what guidance uses; at the default patient the two agree to within about 1%
Worked example
Male, 70 kg, 176 cm, 45 years
10 × 70 = 700; 6.25 × 176 = 1,100; −5 × 45 = −225; male constant +5
700 + 1,100 − 225 + 5 = 1,580 kcal/day
The same patient as a woman: 1,580 − 166 = 1,414 kcal/day. That 166 kcal/day is the sex intercept, and it is the error a page makes if it quietly uses one form for everybody
The published ±10% window round this answer is 1,422 to 1,738 kcal/day, and about one adult in five falls outside it
Per kg: 1,580 ÷ 70 = 22.6 kcal/kg/day — inside ESPEN's 20–25 kcal/kg window and below the 25–30 the ASPEN algorithm gives. The two guidelines disagree about this patient, and the table below says so
Harris-Benedict 1919 on the same patient returns 1,606 kcal/day, 26 kcal/day higher, consistent with the 5% overestimate Mifflin's own paper reported
The four energy equations on this site, and the population each was derived in
| Equation | Derived in | Accuracy, as published | Page |
|---|---|---|---|
| Mifflin-St Jeor, 1990 | 498 healthy adults, 19–78 y, 264 normal weight and 234 obese | More than 10% from measured in 22% of 130 non-hospitalised adults; best of the equations tested and the narrowest error range | This page |
| Harris-Benedict, 1919 and the 1984 Roza-Shizgal revision | Healthy adults, early twentieth century; the revision re-derived against body cell mass | More than 10% from measured in 33% of the same 130 adults; within ±10% in about 65% of men and 57.5% of women in another test group | A separate calculator, with both versions |
| Penn State, PSU(2003b) and PSU(2010) | Mechanically ventilated critical care patients | 67% accurate overall in 202 patients; 69–77% in non-obese subgroups; PSU(2010) 74% at 60 and over with a BMI of 30 or more | A separate calculator |
| Weir, measured | Not predicted — derived from measured gas exchange | The reference method; ESPEN recommends it for ventilated patients (Grade B) | A separate calculator |
Weight-based energy targets, by the guideline that gives each one
| Guideline | Population | Energy target |
|---|---|---|
| ESPEN, intensive care, 2019 | Ventilated adults, indirect calorimetry unavailable | 20–25 kcal/kg/day as the simplest alternative; not exceeding 70% of expenditure in the early phase (rec. 17), then 80–100% of measured after day 3 (rec. 18) |
| ASPEN, nutrition care algorithm | Adult critical care | 25–30 kcal/kg/day from a published predictive or weight-based equation |
| ASPEN, nutrition care algorithm | Critical care with obesity | 11–14 kcal/kg actual weight for a BMI of 30–50; 22–25 kcal/kg ideal weight above 50 |
| ESPEN, geriatrics, 2022 | Older people | A guiding value of 30 kcal/kg/day, individually adjusted (recommendation 1, Grade B) |
| PENG Pocket Guide, 5th ed, 2018 | Hospital inpatients with a BMI of 18.5–30 | 20–25 kcal/kg/day, towards the top of the range with clinical evidence of metabolic stress and no refeeding risk |
The equation is the easy part; the stress factor is where it goes wrong
Mifflin-St Jeor is the equation most guidance now prefers for adults who are not critically ill, and the reason is comparative rather than absolute. In 130 non-hospitalised adults spanning a BMI of 18.8 to 96.8 it was more than 10% away from measured resting metabolic rate in 22% of people, against 33% for Harris-Benedict and 35% for Owen; a systematic review found it predicted within 10% of measured in more non-obese and obese individuals than any other equation, with the narrowest error range. It is the best of a set of estimates, and roughly one adult in five is still mis-estimated by more than a tenth. ESPEN puts the inaccuracy of predictive equations as high as 60%.
So the honest reading is as a population mean for someone of this sex, weight, height and age — a starting point to reconcile with the patient, not a measurement of them. The measurement is indirect calorimetry, which ESPEN recommends for ventilated patients at Grade B; see the Weir equation calculator for what a metabolic cart computes and the respiratory quotient calculator for the ratio it reports alongside.
The part that goes wrong is what happens next. The traditional method multiplies a resting figure by an injury factor and then by an activity factor. The factors in circulation vary widely between sources, most trace back to small twentieth-century series, and multiplying two uncertain multipliers onto an estimate already wrong by a tenth in one person in five compounds the error rather than correcting it. This page therefore prints no stress-factor table, because no row of one could be attributed to a source read for this batch. PENG’s Pocket Guide made the same move in its fifth edition, replacing the factorial method with weight-based estimation at 20 to 25 kcal/kg/day and noting that physical activity is unlikely to exceed 20% above resting in most hospitalised patients. The weight-based targets, each with its guideline, are in the second table.
Two boundaries. This equation takes actual body weight, not a dosing weight: ideal, adjusted and lean body weight exist for drug dosing, and some obesity targets in the table are stated on ideal weight — read which basis a figure uses before applying it. And in anyone who has eaten little for days the energy target is not the first question: see refeeding risk and low phosphate before feeding starts. This page computes a figure and prints the published targets beside it with the guideline each comes from. The prescription is the clinician’s, taken with the patient in front of them.
Frequently asked questions
Which energy equation does current guidance prefer?
For adults who are not critically ill, Mifflin-St Jeor: a systematic review found it “the most reliable, predicting RMR within 10% of measured in more nonobese and obese individuals than any other equation”. For mechanically ventilated critical care patients the Academy of Nutrition and Dietetics recommends the Penn State equations instead, and where it is available ESPEN recommends measuring expenditure by indirect calorimetry rather than predicting it.
How accurate is the Mifflin-St Jeor equation for one person?
Not accurate enough to treat as a measurement. In 130 non-hospitalised adults the prediction was more than 10% away from measured in 22% of them — the best of the equations tested, and still about one person in five. ESPEN describes predictive equations in general as “associated with significant inaccuracy (up to 60%)”.
Should I multiply this figure by a stress or activity factor?
That is the traditional factorial method, and the factors in circulation are not well standardised between sources — which is why no stress-factor table appears here. PENG’s Pocket Guide moved away from it in its fifth edition in favour of weight-based estimation at 20 to 25 kcal/kg/day, and notes that physical activity is unlikely to exceed 20% above resting in most hospitalised patients. The weight-based targets, with their guidelines, are in the table above.
Why does the calculator show the other sex’s answer?
Because the two forms differ by exactly 166 kcal/day at the same weight, height and age, and a calculator that silently used one intercept for everybody would be wrong by that much while looking entirely plausible.
Is resting metabolic rate the same as my daily calorie need?
No. It is the energy spent at rest, awake, in a thermoneutral room, several hours after eating; activity and the thermic effect of food sit on top. It is also not a target: this page computes a figure and prints the published weight-based targets beside it with the guideline each comes from.
Related calculators
References
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. 498 healthy adults aged 19–78, 264 of normal weight and 234 obese; R² = 0.71. Harris-Benedict overestimated measured REE by 5% in this cohort.
- Frankenfield DC, et al. Validation of several established equations for resting metabolic rate in obese and nonobese people. J Am Diet Assoc. 2003;103(9):1152–1159. In 130 adults with a BMI of 18.8 to 96.8, calculated RMR was more than 10% from measured in 22% using Mifflin-St Jeor, 33% using Harris-Benedict and 35% using Owen.
- Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005. Mifflin-St Jeor “was the most reliable, predicting RMR within 10% of measured in more nonobese and obese individuals than any other equation”.
- Singer P, Blaser AR, Berger MM, et al. ESPEN guideline on clinical nutrition in the intensive care unit. Clin Nutr. 2019;38(1):48–79. Recommendations 15 (indirect calorimetry in ventilated patients, Grade B), 17 (not exceeding 70% of energy expenditure in the early phase), 22 (1.3 g/kg protein equivalents), 23 (glucose “should not exceed 5 mg/kg/min”) and 25 (lipids “should not exceed 1.5 g lipids/kg/day”). Predictive equations are “associated with significant inaccuracy (up to 60%)”, with 20–25 kcal/kg/day named as the simplest alternative.
- Parenteral and Enteral Nutrition Group of the British Dietetic Association. A Pocket Guide to Clinical Nutrition. 5th ed. 2018. Replaced the factorial stress-factor method with weight-based estimation at 20–25 kcal/kg/day for a BMI of 18.5–30; activity “unlikely to exceed 20% above REE” in most hospitalised patients; nitrogen from protein using 6.25 “but accept that this is just an approximation”.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/