BMR Calculator

How to use this calculator

1. Choose US Units or Metric Units. Switching converts figures you have already typed rather than clearing them.
2. Enter your age and select your gender.
3. Enter your height and weight.
4. Press Calculate BMR to see your BMR and what you would need each day at six activity levels.

+ Settings holds the three things most people never change: which of the three published equations to use, a body fat percentage for the one that needs it, and whether to answer in Calories or kilojoules.

Other Units opens a pair of small converters above the calculator — one for height, one for weight. They are not a third unit system: use them when your scales read in stones or your tape reads in metres, then type the converted figure into the boxes. The calculator stays on whichever system you chose.

What BMR measures

Your Basal Metabolic Rate is the energy your body spends at complete rest just to keep you alive — breathing, circulating blood, regulating temperature and renewing cells. For most people it accounts for 60–70% of the calories burned in a day, which makes it the foundation for any nutrition plan. Everything you do on top of resting — walking, working, training — adds to it.

The three formulas

The calculator defaults to Mifflin-St Jeor, widely regarded as one of the most accurate for healthy adults. It works in metric units and differs only by a constant at the end for each sex:

Men: BMR = 10 × kg + 6.25 × cm − 5 × age + 5

Women: BMR = 10 × kg + 6.25 × cm − 5 × age − 161

• kg — body weight in kilograms
• cm — height in centimetres
• age — age in years

Enter US figures and the calculator converts pounds and inches before applying the equation.

Two alternatives sit under Settings. Revised Harris-Benedict (Roza and Shizgal, 1984) is the older equation, still widely quoted, and generally reads a little higher: 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age for men, and 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age for women.

Katch-McArdle takes a different route: 370 + 21.6 × lean body mass in kilograms, where lean mass is your weight less your fat. It uses neither height nor age nor sex, because all three are only ever proxies for how much lean tissue you carry — so it is the most accurate of the three if you have a real body fat measurement, and the least useful if you are guessing at one. That is why it is the only equation that asks for a body fat percentage, and the only one that will refuse to answer without one.

A worked example

Take a 35-year-old man who is 180 cm and 80 kg. His BMR is 10 × 80 + 6.25 × 180 − 5 × 35 + 5 = 800 + 1,125 − 175 + 5 = 1,755 calories a day. That is what his body would burn if he spent the whole day at rest, before any movement is added.

From BMR to daily calories

To estimate the calories you actually need, multiply BMR by an activity factor. That product is your Total Daily Energy Expenditure (TDEE), and it is what the table beside the calculator shows. Using the 1,755 BMR above:

Activity level	Factor	Daily calories
Sedentary: little or no exercise	1.2	2,106
Exercise 1-3 times/week	1.375	2,413
Exercise 4-5 times/week	1.465	2,571
Daily exercise or intense exercise 3-4 times/week	1.55	2,720
Intense exercise 6-7 times/week	1.725	3,027
Very intense exercise daily, or physical job	1.9	3,335

"Exercise" here means 15–30 minutes of elevated heart rate activity; "intense exercise" means 45–120 minutes; "very intense exercise" means two hours or more.

The calorie calculator runs this step for you and adds weight-loss and weight-gain targets.

Why BMR varies from person to person

Body size is the biggest driver: a larger body has more tissue to maintain, so it burns more at rest. Sex and age matter too — the equation adds 5 for men and subtracts 161 for women, and takes off 5 for every year of age. Muscle is more metabolically active than fat, which is why two people of the same weight can have different rates.

Accuracy and limitations

• It is an estimate. Mifflin-St Jeor predicts the average for your stats; your true BMR can differ a little either way.
• It does not read body composition. Mifflin-St Jeor and Harris-Benedict use total weight, not your muscle-to-fat split, so very muscular or very lean people may sit off the average — that is the case for switching to Katch-McArdle.
• Healthy adults. Pregnancy, some medical conditions and the extremes of body size are not well captured by a general equation.

For your full daily needs and goal targets, use the calorie calculator; to gauge body composition, see the body fat calculator. This is educational information, not medical advice.