KiloMateBMR calculator
Your BMR (basal metabolic rate) is the energy you burn at rest in a day. Using the Mifflin-St Jeor equation, an 80 kg, 175 cm, 35-year-old man's BMR is about 7,210 kJ (1,724 calories), and a 65 kg, 165 cm, 35-year-old woman's is about 5,630 kJ (1,345 calories). Enter your own details below for yours, in kJ first, then calories.
The formula
Mifflin-St Jeor gives resting energy in calories:
- Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5
- Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161
Multiply by 4.184 to get kJ. Worked through for the man above: 800 + 1,093.75 − 175 + 5 = 1,724 calories, and 1,724 × 4.184 ≈ 7,210 kJ.
The equation comes from a 1990 study that measured resting energy in 498 healthy adults aged 19 to 78, both normal weight and obese. In that study the older Harris-Benedict equations overestimated measured resting energy by about 5%.
From BMR to what you eat
BMR is only the resting part. Add daily movement, training and digesting food and you get your total daily energy expenditure. The TDEE calculator shows that at five activity levels, and the calorie calculator turns it into a daily target with protein. To see what a session at the gym or a walk adds, try the calories burned calculator.
Questions
What is BMR?
Basal metabolic rate: the energy your body uses at complete rest to keep you alive, breathing, circulating blood and holding body temperature. It's the biggest single part of what most people burn in a day.
How do I calculate my BMR?
With the Mifflin-St Jeor equation: 10 × weight in kg, plus 6.25 × height in cm, minus 5 × age, then add 5 for men or subtract 161 for women. The answer is in calories; multiply by 4.184 for kJ. An 80 kg, 175 cm, 35-year-old man comes out at about 1,724 calories (7,210 kJ) a day.
Is BMR the same as RMR or resting energy?
Close enough for a calculator. Strictly, BMR is measured under tighter lab conditions than resting metabolic rate (RMR), but the Mifflin-St Jeor equation was built from measured resting energy and is used for both.
Should I eat my BMR?
No. BMR is what you'd burn lying still all day, so it's below what you actually use once you move, work and train. Your maintenance is your TDEE, which multiplies BMR by an activity factor. Use the TDEE or calorie calculator for an eating target.
How accurate is a BMR calculator?
It's an estimate for a typical person of your size, age and sex. A 2005 systematic review in the Journal of the American Dietetic Association found Mifflin-St Jeor the most reliable of the common equations, but it can still be out for any one person. Muscle mass, genetics and health conditions all shift the real number.
Sources
- Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241–247. DOI
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105(5):775–789. DOI
- Thermochemical calorie = 4.184 J. NIST Special Publication 811, Appendix B.8. NIST
General information only, not medical or dietary advice. Not suitable during pregnancy or breastfeeding, for under-18s, or with a medical condition. Talk to a GP or an Accredited Practising Dietitian.
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