Two quick steps to an estimate of the calories your body burns at complete rest.
By Hammad ShahidLast updated
Basal metabolic rate is the energy your body uses at complete rest, before any movement. The Mifflin-St Jeor equation estimates it as (10 x weight in kg) + (6.25 x height in cm) - (5 x age), then adds 5 for men or subtracts 161 for women. A 32-year-old man of 175 cm and 70 kg comes out at 1,639 kcal; a woman of 165 cm and 62 kg at the same age comes out at 1,330 kcal.
Basal Metabolic Rate (BMR) is an estimate of the minimum calories your body needs to maintain basic physiological functions while at complete rest. This includes energy used for breathing, circulation, brain function, and cellular processes, not physical activity or digestion after meals.
FitQuota uses the Mifflin-St Jeor equation, one of the most widely referenced BMR formulas in nutrition science. The calculator runs three steps in order, using the values you entered above.
1. Convert your measurements to metric
weight in kg = lb × 0.453592, and height in cm = (ft × 30.48) + (in × 2.54)
2. Apply the Mifflin-St Jeor equation
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5 for men, or − 161 for women
3. Round to a whole calorie
BMR = round(BMR)
Enter a body fat percentage above and the calculator runs a second equation alongside Mifflin-St Jeor. Katch-McArdle ignores your total weight and predicts from lean mass instead:
1. Work out lean mass
lean mass = weight in kg × (1 − body fat % ÷ 100)
2. Apply Katch-McArdle
BMR = 370 + (21.6 × lean mass in kg)
The two equations disagree in a predictable direction. Someone lean for their weight gets a higher figure from Katch-McArdle, because muscle is doing the burning; someone carrying more fat gets a lower one. A 70 kg person at 15% body fat has 59.5 kg of lean mass and a Katch-McArdle BMR of 1,655 kcal. The same 70 kg person at 30% has 49 kg of lean mass and 1,428 kcal, a gap of 227 from the identical body weight.
That sensitivity is the catch. Katch-McArdle is only as good as the body fat figure you feed it, and if that figure came from a body fat calculator rather than a DEXA scan, it carries an error of several percentage points, which this equation then multiplies. Use it when you have a measured body composition, and treat Mifflin-St Jeor as the default otherwise.
For your purposes, yes. Resting metabolic rate is measured under less strict conditions than a true basal rate, which requires an overnight fast, complete rest and a controlled temperature, so RMR comes out slightly higher, usually by a few percent.
No prediction equation is precise enough for that gap to matter. Mifflin-St Jeor was itself derived against measured resting values, so a calculator labelled BMR and one labelled RMR are estimating the same thing with the same arithmetic. The distinction belongs in a metabolic ward rather than in a calorie target.
Mifflin-St Jeor is not the only BMR formula, and a calculator elsewhere may be using a different one without saying so.
The Harris-Benedict equation dates from 1919 and was revised in 1984. Like Mifflin-St Jeor it predicts from weight, height, age and sex, and it usually comes out a little higher: for a 32-year-old man of 175 cm and 70 kg the original gives 1,689 kcal against Mifflin-St Jeor’s 1,639.
The Katch-McArdle and Cunningham equations predict from lean body mass instead of total weight, so they need a body fat percentage. Katch-McArdle is 370 + (21.6 × lean mass in kg) and Cunningham is 500 + (22 × lean mass in kg). At 70 kg and 20% body fat that is 56 kg of lean mass, which gives 1,580 kcal and 1,732 kcal respectively. They suit people who know their body composition well, and inherit every error in the body fat figure they are fed.
The Schofield equations predict from body weight within age bands, with a separate equation for each, and are widely used in clinical and public health settings. All ten of them, and a calculator that applies the one matching your age, are on the Schofield equation calculator.
None of this makes Mifflin-St Jeor the only right answer. The gap between equations is real but modest next to the activity choice that follows, which why TDEE calculators give different results sets out with the full comparison.
BMR is a foundation for estimating total daily calorie needs. By applying an activity multiplier to BMR, you can estimate Total Daily Energy Expenditure (TDEE) a more practical number for meal planning. Try our TDEE Calculator or Calorie Calculator to take the next step.
BMR is often discussed alongside Resting Metabolic Rate (RMR). Both measure calories burned at rest, but RMR is typically measured under slightly less strict conditions and may be a few percent higher. For everyday planning, BMR and RMR estimates are often used similarly.
That the Schofield equations were derived from a screening of fifty years of published data, including subjects from developing countries.
The Mifflin-St Jeor equation used to estimate resting energy expenditure.
Resting metabolism varies with genetics, muscle mass and body composition, so this is an estimate rather than a measurement of your own metabolism.
The equation was derived from 498 adults aged 19 to 78, and was not developed for children or teenagers. Under-19s should speak to a doctor or a registered dietitian rather than rely on this figure.
If you have a medical condition, are pregnant or breastfeeding, have a history of eating disorders, or are making a significant change to how you eat or train, consider speaking with a qualified healthcare professional.
Guide
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