BMR 計算機（基礎代謝率）
三種公式並列比較：Mifflin-St Jeor、修訂版 Harris-Benedict 與 Katch-McArdle。
BMR
Mifflin-St Jeor
1780kcal/day
Harris-Benedict
1854kcal/day
What BMR is and why it matters
Basal Metabolic Rate (BMR) is the rate at which your body burns calories to stay alive and functioning at complete rest. It powers your brain, your beating heart, your liver and kidneys, and your basic cellular maintenance. Even on a day where you do absolutely nothing, you burn roughly your BMR.
BMR is the foundation number underneath every calorie target: every TDEE estimate, every cut, every bulk starts by predicting BMR and then layering on activity factors. Get BMR wrong and every number downstream is wrong. That’s why this calculator shows you three formulas at once.
The three formulas
Mifflin-St Jeor (1990)
The current standard. Validated against indirect calorimetry in 498 subjects (251 men, 247 women) representing a healthy modern adult population.
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161For non-athletes between BMI 18.5 and 35, Mifflin-St Jeor predicts measured BMR within 3% in most individuals.
Harris-Benedict revised (Roza & Shizgal, 1984)
A 1980s update of the original 1919 equation, fit to a more modern data set.
Men: BMR = 88.362 + (13.397 × weight(kg)) + (4.799 × height(cm)) − (5.677 × age)
Women: BMR = 447.593 + (9.247 × weight(kg)) + (3.098 × height(cm)) − (4.330 × age)It overestimates Mifflin-St Jeor by roughly 5–10% for most adults. Useful as a comparison; not our default.
Katch-McArdle (lean-mass based)
The most accurate of the three if you know your body fat percentage — and especially the right choice for highly muscular or very lean individuals.
LBM = weight(kg) × (1 − body_fat / 100)
BMR = 370 + 21.6 × LBM(kg)It does not use sex, age, or height — only lean body mass. The reasoning: muscle is roughly 13× more metabolically active than fat at rest, so most of the variance in BMR across people of the same mass is explained by differences in lean mass. Katch-McArdle is the formula bodybuilders and physique athletes use during contest prep.
A worked example
A 30-year-old woman, 65 kg, 168 cm, 24% body fat:
- Mifflin-St Jeor: 10×65 + 6.25×168 − 5×30 − 161 = 650 + 1050 − 150 − 161 = 1389 kcal
- Harris-Benedict: 447.593 + 9.247×65 + 3.098×168 − 4.330×30 = 447.593 + 601.06 + 520.46 − 129.9 = 1439 kcal
- Katch-McArdle: LBM = 65 × 0.76 = 49.4 kg → 370 + 21.6 × 49.4 = 1437 kcal
The three estimates span 50 kcal, or about 3.5%. That’s a typical spread for someone within the formulas’ validation range.
A 35-year-old male powerlifter, 100 kg, 178 cm, 14% body fat:
- Mifflin-St Jeor: 10×100 + 6.25×178 − 5×35 + 5 = 1000 + 1112.5 − 175 + 5 = 1942 kcal
- Harris-Benedict: 88.362 + 13.397×100 + 4.799×178 − 5.677×35 = 88.362 + 1339.7 + 854.22 − 198.7 = 2084 kcal
- Katch-McArdle: LBM = 100 × 0.86 = 86 kg → 370 + 21.6 × 86 = 2228 kcal
Now the spread is 290 kcal, or about 13%. Mifflin-St Jeor and Harris-Benedict undershoot because they don’t see his lean mass — they see only his weight, height, age, and sex, which describe a “normal” 100 kg male body. Katch-McArdle is the right answer here.
Which formula should you use?
| Your profile | Recommended formula |
|---|---|
| Sedentary or moderately active adult, BMI 18–35, body composition unknown | Mifflin-St Jeor |
| You know your body fat percentage and you’re highly muscular (lifter, athlete) | Katch-McArdle |
| You know your body fat percentage and you’re very lean (BF < 12% men / 18% women) | Katch-McArdle |
| You want a sanity check against a number a doctor or dietitian gave you | Compare all three |
How to use this calculator
- Enter age, sex, weight, and height.
- Optionally enter body fat percentage to enable Katch-McArdle. If you don’t know it, run the body fat calculator first.
- Toggle metric or imperial.
- Read the three estimates side by side. Use the formula that best fits your profile.
How BMR changes with age
Recent metabolic research (Pontzer et al., 2021, Science) traces BMR across the human lifespan and finds something surprising: BMR per kg of lean mass is remarkably stable from age ~20 to age ~60. The “metabolism slows down with age” myth is, in large part, a story about losing lean mass — not a story about your cells burning slower.
The implications:
- Your BMR doesn’t drop because you’re 40. It drops because, between 25 and 40, you lost 4 kg of lean mass.
- Resistance training is the cleanest way to defend BMR as you age. Two heavy sessions per week is enough to preserve most lean mass into your 60s.
- The age coefficient in Mifflin-St Jeor (-5 kcal per year) is mostly a stand-in for that progressive lean-mass loss in a sedentary population. If you keep training, the real-world effect is smaller.
What BMR is not
A few common misconceptions:
- BMR is not the same as RMR. Resting Metabolic Rate is what your watch and most online calculators actually estimate; it’s roughly 5–10% higher than true BMR because it doesn’t require strict fasting and immediately-post-sleep conditions. The difference rarely matters for nutrition planning.
- BMR is not what you should eat to lose weight. Eating below BMR for extended periods causes hormonal and adaptive disruption. Use TDEE − 500 kcal as a deficit target, not BMR − anything.
- BMR is not destiny. It changes with body composition, training status, body temperature, illness, sleep, and stress. Build the habits and the number follows.
常見問題
What is BMR exactly?
Your Basal Metabolic Rate is the number of calories your body burns at **complete rest**, in a temperature-controlled environment, in the morning, after a 12-hour fast, when fully awake but lying still. In real life, you almost never measure BMR directly — you measure Resting Metabolic Rate (RMR), which is roughly 5–10% higher because it doesn't require the strict fasting and post-sleep conditions.
Which BMR formula should I use?
For most non-athletes, **Mifflin-St Jeor** (1990) is the most accurate published equation — typically within 3% of measured BMR. If you know your **lean body mass**, switch to **Katch-McArdle**, which scales BMR with fat-free mass and is more accurate for very lean or very muscular individuals.
Why is BMR a different number than TDEE?
BMR is just one piece of TDEE. TDEE = BMR + thermic effect of food (~10%) + exercise calories + non-exercise activity. For a typical sedentary adult, BMR is about 60–70% of TDEE. For an active adult, BMR can drop below 50% of TDEE.
Does my BMR change as I age?
Yes, but mostly because lean mass declines with age, not because of a separate "metabolic slowdown." Resistance training preserves lean mass and therefore preserves BMR. Recent research suggests BMR per kg of lean mass stays remarkably stable from about 20 to 60 years old.
Why does Harris-Benedict give a higher number than Mifflin-St Jeor?
The original Harris-Benedict equation was developed in 1919 and overestimates modern populations by 5–15%. The "revised Harris-Benedict" (Roza & Shizgal, 1984) corrects some of that, but Mifflin-St Jeor (developed on a more representative sample in 1990) is still slightly more accurate for most adults.
How accurate are these BMR formulas?
All three are predictive equations fit to indirect-calorimetry data from healthy adults. Within their validation range, expect ±10% error in 80% of individuals and ±15% error in 95%. They are screening tools, not measurements. For an actual BMR number, you need an indirect calorimetry test in a clinic.