Mifflin–St Jeor calculator: resting energy vs daily energy estimates
Understand the Mifflin–St Jeor equation, reproduce a resting-energy example, and see why changing an activity multiplier creates a scenario rather than a measurement.
Identify the quantity the equation predicts
The Mifflin–St Jeor equation predicts resting energy expenditure, usually abbreviated REE. Its original 1990 study used measurements from 498 healthy participants aged 19–78, with resting expenditure measured by indirect calorimetry. A calculator applies a relationship derived from those observations to the measurements you enter. It does not measure your metabolism. Although BMR calculator is a common name, basal metabolic rate refers to expenditure under specific standardized conditions. Small Hours labels the result estimated resting energy to preserve the distinction. Begin by identifying that output before looking at the separate whole-day scenario or comparing it with another calculator.
Reproduce the arithmetic with explicit units
The simplified equation is 10 × weight in kilograms + 6.25 × height in centimeters − 5 × age in years + the selected coefficient. The original male coefficient is +5 and the female coefficient is −161. For an illustrative input of 77 kg, 178 cm and age 44 with coefficient +5, the calculation is 770 + 1,112.5 − 220 + 5, or 1,667.5 kcal/day. The BMR and daily energy estimator reproduces that result and displays 6,976.8 kJ/day for the same resting estimate. The conversion uses 4.184 kilojoules per kilocalorie; both outputs retain the same per-day period.
Keep resting energy separate from whole-day expenditure
Total daily expenditure includes more than resting expenditure, including physical activity and the metabolic response to food. FAO’s human-energy report describes physical activity level as total energy expenditure divided by basal metabolic rate over a matching period. This tool uses an editable multiplier on a predicted resting value to illustrate the general scaling idea. It does not measure that ratio or implement a complete energy-assessment protocol. Do not interpret the resting output as the total for an ordinary day, or the multiplied output as a measured total. Read the result labels together with the assumptions that produced them.
Compare two multipliers without pretending to know the answer
Hold the illustrative resting estimate of 1,667.5 kcal/day constant. At multiplier 1.3, the daily scenario is 2,167.75 kcal/day, displayed as 2,167.8. At 1.8, it becomes 3,001.5 kcal/day. The 833.75 difference comes entirely from the changed multiplier; the tool has received no new information about occupation, movement or training. That is a useful sensitivity comparison because it reveals how much the assumption influences the output. It does not establish that either multiplier fits the example person. Typing more decimal places into the multiplier would produce a more detailed number without supplying the missing activity evidence.
| Quantity | Calculation | kcal/day |
|---|---|---|
| Resting estimate | 70 kg, 175 cm, age 30, coefficient +5 | 1,648.75 |
| Daily scenario, multiplier 1.4 | 1,648.75 × 1.4 | 2,308.25 |
| Daily scenario, multiplier 1.6 | 1,648.75 × 1.6 | 2,638.00 |
Equation predictions and entered multipliers are not measured expenditure or a prescribed intake.
Treat coefficient choice and input bounds as visible limitations
With the same weight, height and age, selecting −161 instead of +5 changes the resting estimate from 1,667.5 to 1,501.5 kcal/day. The 166 difference follows directly from the published coefficients. These two options do not model every individual physiology or resolve their applicability in every clinical situation. Small Hours accepts whole-number ages 19–78, weight 30–300 kg, height 120–230 cm and multipliers 1–2.5. The age restriction matches the original cohort; the measurement limits are usability checks. Passing those checks is not evidence that a person’s prediction is accurate throughout the accepted ranges.
Distinguish an illustration from a personal energy assessment
The default multiplier of 1.4 is an illustration, not a conclusion about your activity. NIDDK’s separate Body Weight Planner describes physical activity levels and models weight changes with additional assumptions; Small Hours does not implement that planner. This estimator also excludes pregnancy, breastfeeding and clinical-illness assessment. It supplies no personal prediction interval, measured activity record or modeled weight trajectory. Comparing several online equations may reveal different assumptions, but agreement between their outputs does not independently validate an individual result. If an energy assessment is needed for a health decision, a qualified professional can consider context and whether appropriate measurement is required.
Use the tool to examine assumptions, then label the result accurately
For a reproducible educational calculation, record weight and height units, age, selected coefficient and the multiplier. Read the resting estimate first, then change only the multiplier to inspect sensitivity. If you compare another result, check whether it reports resting expenditure, basal expenditure, a daily scenario or recommended intake, since those labels refer to different questions. Save the inputs alongside any copied number and retain the word estimated. Neither Small Hours output is a dietary prescription, a weight-loss target or a minimum safe intake. Subtracting a fixed amount would add a new assumption that this calculator has not assessed or supported.