How to use the bmr calculator
- Enter your age in years and select your biological sex.
- Type your weight in kilograms and height in centimeters.
- Optionally add your body fat percentage to enable the Katch-McArdle equation.
- Read the estimated basal metabolic rate from each formula below.
How the three equations work
This BMR calculator applies three peer-reviewed formulas. The Mifflin-St Jeor equation (1990) is considered the most accurate for the general population:
Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5
Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161
For an 80 kg, 180 cm, 30-year-old male: (10 x 80) + (6.25 x 180) - (5 x 30) + 5 = 800 + 1125 - 150 + 5 = 1780 kcal/day.
The revised Harris-Benedict equation (Roza and Shizgal, 1984) updates the original 1919 coefficients:
Men: BMR = 88.362 + (13.397 x weight) + (4.799 x height) - (5.677 x age)
Women: BMR = 447.593 + (9.247 x weight) + (3.098 x height) - (4.330 x age)
The Katch-McArdle formula uses lean body mass (LBM) instead of total weight, making it useful when body fat is known:
BMR = 370 + (21.6 x LBM in kg), where LBM = weight x (1 - body fat / 100).
Reference table: BMR by weight (Mifflin-St Jeor, male, 175 cm, age 30)
The table below shows how weight affects the resting metabolic rate estimate for a 30-year-old male who is 175 cm tall, using the Mifflin-St Jeor equation.
| Weight (kg) | BMR (kcal/day) |
|---|---|
| 60 | 1,549 |
| 70 | 1,649 |
| 80 | 1,749 |
| 90 | 1,849 |
| 100 | 1,949 |
| 110 | 2,049 |
Each additional 10 kg adds exactly 100 kcal/day because the weight coefficient is 10.
BMR versus RMR
A basal metabolic rate calculator estimates the energy needed to sustain vital functions while completely at rest, fasted, in a thermoneutral environment. Resting metabolic rate (RMR) is measured under less strict conditions and is typically about 10 percent higher. In practice, many people use the terms interchangeably, and an RMR calculator will often apply the same equations shown here. If you need a more precise number, indirect calorimetry in a clinical setting is the gold standard.
From BMR to daily calories
Your BMR is only part of the picture. To estimate total daily energy expenditure, multiply your BMR by an activity factor: sedentary (1.2), lightly active (1.375), moderately active (1.55), very active (1.725) or extra active (1.9). Once you have that number, you can use a calorie deficit calculator to plan weight changes, or a TDEE calculator for a combined workflow. Pairing this with a BMI calculator helps contextualize your weight relative to height.
Common mistakes to avoid
Using pounds or inches without converting first will produce wildly incorrect results. Always enter weight in kilograms and height in centimeters. Another frequent error is applying these adult formulas to children; they are validated only for ages 15 and older. Finally, remember that the output is an estimate, not medical advice. Talk to a doctor or registered dietitian before making major diet changes. Individual variation due to genetics, hormone levels, organ mass and medication can shift actual metabolic rate by 10 to 15 percent in either direction.
Worked examples
| Example | Input | Result |
|---|---|---|
| Average male | Age (years): 30; Sex: male; Weight (kg): 80; Height (cm): 180 | Mifflin-St Jeor: 1,780 kcal/day; Revised Harris-Benedict: 1,854 kcal/day |
| Average female | Age (years): 30; Sex: female; Weight (kg): 65; Height (cm): 165 | Mifflin-St Jeor: 1,370 kcal/day; Revised Harris-Benedict: 1,430 kcal/day |
| With body fat | Age (years): 25; Sex: male; Weight (kg): 90; Height (cm): 185; Body fat % (optional): 15 | Mifflin-St Jeor: 1,936 kcal/day; Revised Harris-Benedict: 2,040 kcal/day; Katch-McArdle: 2,022 kcal/day |
| Older adult | Age (years): 65; Sex: female; Weight (kg): 70; Height (cm): 160; Body fat % (optional): 30 | Mifflin-St Jeor: 1,214 kcal/day; Revised Harris-Benedict: 1,309 kcal/day; Katch-McArdle: 1,428 kcal/day |
FAQ
What is a BMR calculator?
A BMR calculator estimates your basal metabolic rate: the number of calories your body needs each day to maintain basic physiological functions like breathing, circulation and cell production while at complete rest.
Which equation is the most accurate?
The Mifflin-St Jeor equation is generally considered the most accurate for healthy adults. If you know your body fat percentage, the Katch-McArdle formula may be more precise because it accounts for lean mass directly.
Is BMR the same as RMR?
They are similar but not identical. Basal metabolic rate is measured under stricter fasting and rest conditions. Resting metabolic rate (RMR) is slightly higher, usually by about 10 percent, because it is measured under less controlled circumstances.
Can I use this metabolism calculator if I am under 15?
No. The Mifflin-St Jeor, revised Harris-Benedict and Katch-McArdle equations were developed and validated on adult populations. For children and adolescents, consult a pediatrician or use age-specific predictive equations.
Why does the Katch-McArdle result differ from the others?
Katch-McArdle uses lean body mass rather than total weight. Since muscle tissue is more metabolically active than fat tissue, two people with the same weight but different body fat percentages will get different Katch-McArdle results.
How do I use my BMR to lose weight?
Multiply your BMR by an activity factor to estimate total daily energy expenditure, then subtract 300 to 500 calories per day for gradual weight loss. A calorie deficit calculator can help with the math.