BMR Calculator - 無料オンライン電卓

Basal Metabolic Rate is the energy your body burns just keeping you alive - beating heart, breathing lungs, functioning brain, maintaining body temperature, regenerating cells. It accounts for 60-75% of total daily calorie expenditure for most adults, dwarfing the calories burned by exercise (typically 10-20%) and the thermic effect of food (about 10%). Understanding your BMR is the starting point for any structured nutrition or fitness plan, whether you're trying to lose weight, build muscle, or maintain.

This calculator uses the Mifflin-St Jeor equation, which research consistently shows is the most accurate predictive formula for the modern adult population. Multiple studies have compared it against indirect calorimetry (gold-standard lab measurement) and found Mifflin-St Jeor to be within ±10% of measured BMR for 82% of adults - better accuracy than Harris-Benedict (1919, revised 1984) which tends to overestimate by ~5%. For the small percentage of outliers (very lean athletes or very heavy individuals), direct measurement via lab calorimetry or a body composition scan is more accurate.

The Mifflin-St Jeor equation uses four inputs: weight (kg), height (cm), age (years) and gender. For men: BMR = 10W + 6.25H − 5A + 5. For women: BMR = 10W + 6.25H − 5A − 161. The gender constant captures the systematic difference in lean body mass between average men and women - men carry more muscle, which burns more calories at rest than fat. Age is subtracted because BMR declines by roughly 1-2% per decade after age 20, primarily due to muscle loss (sarcopenia) and hormonal changes.

BMR predictive equations have one major limitation: they assume average body composition for the given height/weight/age. A 70 kg male at 25% body fat has lower BMR than a 70 kg male at 12% body fat because muscle tissue burns ~13 kcal/kg/day while fat tissue burns ~4 kcal/kg/day. If you know your body fat percentage, the Katch-McArdle formula (BMR = 370 + 21.6 × lean body mass kg) is more accurate. For general use without body fat data, Mifflin-St Jeor remains the best choice.

To convert BMR to total daily calories burned (TDEE), multiply by an activity factor: 1.2 for sedentary (desk job, no exercise), 1.375 for lightly active (light exercise 1-3 days/week), 1.55 for moderately active (3-5 days/week), 1.725 for very active (6-7 days/week), 1.9 for extremely active (athletes, physical labour + training). The TDEE is your daily calorie target for maintenance; subtract 500 kcal for ~0.5 kg/week weight loss, add 250-500 for muscle gain.