How to calculate BMR by hand: the Mifflin-St Jeor equation in pounds and inches

What is BMR, and which equation should you use?

BMR stands for basal metabolic rate. It is the energy your body needs just to stay alive at rest, for breathing, circulation and keeping cells working. It is not the number of calories you burn in a day, because it leaves out movement and exercise. For that bigger number, see the guide to how many calories you burn in a day.

Research papers use slightly different names. The equation below was published for resting energy expenditure, and the systematic review that tested it speaks of resting metabolic rate.¹² This guide uses BMR for the same idea and keeps the equation exactly as published.

Four equations are common in clinical practice: Harris-Benedict, Mifflin-St Jeor, Owen and the World Health Organization set. A systematic review compared them in healthy non-obese and obese adults. It concluded that Mifflin-St Jeor was the most reliable, predicting within 10% of measured in more people than any other equation, with the narrowest error range.² That is why this page uses it.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) also offers a Body Weight Planner, an online tool for adults to build calorie and activity plans toward a goal weight.³ This page is the opposite: no tool, just the arithmetic, so you can see where the number comes from.

The equation, step by step

The published version uses kilograms and centimeters. Mifflin and colleagues derived it from 498 healthy adults, 247 women and 251 men, aged 19 to 78, whose resting energy was measured by indirect calorimetry.¹ The simplified forms by sex are:

Most US scales and tape measures use pounds and inches, so you convert first. The factors are standard unit conversions:

1. Convert weight. Multiply pounds by 0.4536 to get kilograms.
2. Convert height. Multiply inches by 2.54 to get centimeters.
3. Multiply. Take 10 times the kilograms and 6.25 times the centimeters.
4. Subtract age. Take 5 times your age in years and subtract it.
5. Add the sex term. Add 5 for men or subtract 161 for women.

Three worked examples in pounds and inches

The people below are made up for the arithmetic. Their weights, heights and ages are examples, not data.

Example 1: a 35-year-old man, 180 lb, 70 in

Weight: 180 lb × 0.4536 = 81.65 kg. Height: 70 in × 2.54 = 177.8 cm. Weight term: 10 × 81.65 = 816.5. Height term: 6.25 × 177.8 = 1,111.25. Age term: 5 × 35 = 175. Total: 816.5 + 1,111.25 minus 175 + 5 = 1,757.75. The estimate is about 1,758 kilocalories per day.

Example 2: a 42-year-old woman, 150 lb, 65 in

Weight: 150 lb × 0.4536 = 68.04 kg. Height: 65 in × 2.54 = 165.1 cm. Weight term: 680.4. Height term: 6.25 × 165.1 = 1,031.875. Age term: 5 × 42 = 210. Total: 680.4 + 1,031.875 minus 210 minus 161 = 1,341.275. The estimate is about 1,341 kilocalories per day.

Example 3: a 65-year-old man, 200 lb, 68 in

Weight: 200 lb × 0.4536 = 90.72 kg. Height: 68 in × 2.54 = 172.72 cm. Weight term: 907.2. Height term: 6.25 × 172.72 = 1,079.5. Age term: 5 × 65 = 325. Total: 907.2 + 1,079.5 minus 325 + 5 = 1,666.7. The estimate is about 1,667 kilocalories per day.

What moves the result, and by how much

Because the equation is a straight line, you can read the effect of each input from its coefficient. Ten times the kilograms means each kilogram adds 10 kilocalories.¹ One pound is 0.4536 kilograms, so one pound adds about 4.5 kilocalories. One inch is 2.54 centimeters, so one inch adds 6.25 × 2.54, about 15.9 kilocalories. Each year of age subtracts 5.¹

Notice what is missing. The equation does not know how much of your weight is muscle and how much is fat. Two people with the same weight, height, age and sex get the same number, whatever their body composition. The authors tested adding relative body weight and body-weight distribution and found it did not significantly improve prediction.¹

How accurate is the estimate?

Better than the older formulas, but not exact. The 1990 paper found that the Harris-Benedict equations, derived in 1919, overestimated measured resting energy expenditure by 5%.¹ The systematic review found Mifflin-St Jeor within 10% of measured in more non-obese and obese people than any other equation tested.² It also warns of noteworthy errors and limitations when the equation is applied to an individual.²

Here is what a 10% band means for Example 1. Ten percent of 1,758 is about 176. A person whose estimate is 1,758 could measure anywhere from roughly 1,582 to 1,934 and still be inside the 10% band. That is a spread of about 350 kilocalories, which is large if you are fine-tuning a diet.

The review is also frank about who was left out. Older adults and US-residing ethnic minorities were underrepresented in the development of the equations and in validation studies, and the authors advise a high level of suspicion about accuracy for groups that are greatly underrepresented.² The sample in the original paper ran from age 19 to 78, with an average of 45.¹

The review states that errors would be removed by measuring resting metabolic rate with indirect calorimetry under an evidence-based protocol.² That is a laboratory or clinic test. At home, treat your result as a starting estimate and adjust it against what you observe over several weeks.

A second route: from fat-free mass

The same paper reports that fat-free mass (everything that is not fat) was the best single predictor of resting energy expenditure, with the relationship REE = 19.7 × fat-free mass in kilograms + 413.¹ Weight alone also correlated closely: REE = 15.1 × weight in kilograms + 371.¹

An example, with an assumed body-fat figure so the arithmetic works. Take the 180-pound man from Example 1 and suppose a body fat of 20%. Fat-free mass is 80% of 180, which is 144 lb. In kilograms, 144 × 0.4536 = 65.32. Then 19.7 × 65.32 = 1,286.8, and adding 413 gives about 1,700 kilocalories per day.

That is about 58 below the 1,758 from the weight-height-age equation. The gap is small here, but it shows why a body-composition number can change the estimate. It also shows the catch: the fat-free mass figure is only as good as the method that produced it. A scale that estimates body fat by electrical impedance gives an estimate, not a measurement, so the BMR derived from it inherits that error. See the guide to body fat percentage for how those numbers are produced.

What BMR is not, and how to use the number

• It is not your daily calorie need. Daily need adds movement, exercise and the energy used to digest food. Use the calorie guide for that.
• It is not a target to eat. Eating exactly your estimate is not a plan, and the estimate may be off by 10% either way.²
• It is not a health score. A high or low estimate says nothing about whether you are well.
• It is not the same as “metabolic age”, a figure some scales show. See metabolic age explained.

None of this replaces advice from a health professional, especially if you are pregnant, breastfeeding, under 18, or managing a medical condition. The NIDDK notes its own planner is for adults and not for younger people or for pregnant or breastfeeding women.³

Frequently asked questions