How to use it
- Choose US or metric units and enter sex, age, weight and height.
- Read the Mifflin–St Jeor and Harris–Benedict results side by side.
- If you know your body fat percentage, tick the box and enter it to add Katch–McArdle and your lean body mass.
The three equations
Weight in kilograms, height in centimetres, age in years; results in kcal a day.
Mifflin–St Jeor (Mifflin, St Jeor et al., 1990):
- men: 10 × weight + 6.25 × height − 5 × age + 5
- women: 10 × weight + 6.25 × height − 5 × age − 161
Harris–Benedict, revised by Roza and Shizgal (1984):
- men: 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
- women: 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age
Katch–McArdle (from Katch and McArdle’s exercise physiology texts):
- 370 + 21.6 × lean body mass, where lean mass = weight × (1 − body fat % ÷ 100)
US units are converted exactly: 1 lb = 0.45359237 kg, 1 in = 2.54 cm.
Worked example
A 30-year-old man, 70 kg, 175 cm, 15 % body fat:
- Mifflin–St Jeor: 700 + 1,093.75 − 150 + 5 = 1,649 kcal
- Harris–Benedict: 88.362 + 937.79 + 839.825 − 170.31 = 1,696 kcal
- lean mass 70 × 0.85 = 59.5 kg; Katch–McArdle: 370 + 21.6 × 59.5 = 1,655 kcal
Good to know
- BMR is measured lying still after a night’s sleep and fasting; resting energy expenditure (REE) is a looser version of the same idea. The equations estimate either and are often used interchangeably.
- Individual results can differ from a lab measurement by 10 % or more. Illness, thyroid disorders and some medicines change metabolism; a doctor can order indirect calorimetry when an exact figure matters.
- To plan meals, turn BMR into daily calories with an activity factor.