健康与健身

BMI计算器

计算体质指数和健康体重范围

使用方法

Select your preferred unit system: 公制 (kg, cm) or 英制 (lb, ft/in).
Enter your height and weight.
Enter your age and sex for a more accurate healthy weight range.
您的BMI将自动计算并显示类别和健康范围。

Note: BMI is a screening tool, not a diagnostic tool. Consult a healthcare provider for a complete assessment.

公式

BMI = weight(kg) / height²(m)

英制：BMI = 703 × 体重(lb) / 身高²(in)

Underweight< 18.5

Normal weight18.5 – 24.9

Overweight25 – 29.9

Obese (Class I)30 – 34.9

Obese (Class II)35 – 39.9

Obese (Class III)≥ 40

什么是 BMI 以及为什么它很重要？

Body Mass Index (BMI) is a numerical value derived from your height and weight that serves as a widely adopted screening metric for weight-related health risks. Developed in the early 19th century by Belgian mathematician Adolphe Quetelet and later popularized in clinical medicine, BMI has become the global standard for classifying adults into weight categories—underweight, healthy weight, overweight, and obese. Today, it is endorsed by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) as an affordable, non-invasive first-line assessment tool.

While BMI does not directly measure body fat percentage, research published in journals such as the International Journal of Obesity consistently shows that BMI is moderately correlated with more precise measures like dual-energy X-ray absorptiometry (DEXA) scans. For most adults, a BMI between 18.5 and 24.9 kg/m² is considered the healthy range associated with the lowest risk of weight-related disease.

BMI是如何计算的？公式背后的科学

The BMI formula is elegantly simple: your body weight in kilograms divided by the square of your height in metres. In imperial units, the same result is achieved by multiplying 703 by your weight in pounds divided by height in inches squared. Despite its simplicity, the formula encapsulates a useful relationship between body size and health risk for population-level screening.

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Metric: BMI = weight (kg) ÷ height² (m)
Imperial: BMI = 703 × weight (lb) ÷ height² (in)

Beyond raw BMI, our calculator also computes BMI素—the ratio of your BMI to the upper limit of normal (25 kg/m²). A BMI Prime below 1.0 indicates you are within or below the healthy range, while values above 1.0 signal overweight or obesity. The Wikipedia article on BMI Prime provides an in-depth discussion of this metric and its cross-population utility. The calculator additionally shows the 彭德拉指数 (kg/m³), which scales more appropriately for very tall or very short individuals.

BMI 类别解释：从体重不足到严重肥胖

The WHO classifies BMI into six distinct categories for adults aged 20 and older. Each bracket carries different health implications and recommended clinical actions:

< 18.5

体重不足

可能预示着营养不良、荷尔蒙失衡或饮食失调。咨询医疗保健提供者。

18.5 – 24.9

健康体重

与体重相关的慢性疾病的风险最低。通过均衡饮食和活动来维持。

25 – 29.9

超重

2 型糖尿病、高血压和心血管疾病的风险增加。建议改变生活方式。

30 – 34.9

肥胖（I级）

高风险。建议进行医学评估和结构化体重管理计划。

35 – 39.9

肥胖（II级）

风险非常高。通常被称为“严重肥胖”。强烈建议专业护理。

≥ 40

肥胖（III级）

合并症的极大风险。以前称为“病态肥胖”。立即进行临床干预至关重要。

Children & Teens (ages 2–20): BMI is interpreted differently. The CDC uses age- and sex-specific percentiles rather than fixed cutoffs. Healthy weight falls between the 5th and 85th percentile; a BMI at or above the 95th percentile is classified as obese. See the CDC's Child & Teen BMI calculator for age-adjusted results.

BMI 异常的健康风险：研究结果

⚠️ Risks of High BMI (Overweight & Obesity)

A BMI above 25 kg/m² has been linked in meta-analyses to a significantly elevated risk of developing serious chronic conditions. The Wikipedia overview of obesity health effects summarises decades of epidemiological evidence:

Type 2 diabetes — up to 7× higher lifetime risk
Coronary artery disease & stroke
Hypertension (high blood pressure)
Obstructive sleep apnea
Non-alcoholic fatty liver disease (NAFLD)
Certain cancers (breast, colon, endometrial, kidney)
Osteoarthritis of the knee and hip
Reduced psychological wellbeing & quality of life

❄️ 低体重指数（体重过轻）的风险

Being underweight (BMI < 18.5) carries its own set of serious health consequences, often overlooked compared to obesity-related discourse:

Malnutrition and micronutrient deficiencies
Anemia and impaired immune function
Osteoporosis and increased fracture risk
Delayed wound healing
Fertility issues and menstrual irregularities
Muscle wasting (sarcopenia)
Greater surgical complication rates
All-cause mortality risk comparable to Class I obesity

BMI 限制：这个数字不能告诉您什么

BMI is a population-level screening metric, not a personalised diagnostic tool. Understanding its limitations helps you put your result in the right context:

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Athletes & Highly Muscular Individuals — Muscle is denser than fat. A trained athlete may have a BMI in the "overweight" range while carrying very little body fat. Use our 体脂率计算器 for a more accurate picture.

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Older Adults — Ageing naturally shifts body composition toward higher fat and lower muscle mass, even at the same BMI. Seniors often need additional assessments such as waist circumference or grip strength tests.

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Ethnic Differences — Research shows that people of South, East, and Southeast Asian descent face elevated metabolic risk at lower BMI thresholds. The WHO suggests using a cutoff of 23 kg/m² for overweight and 27.5 kg/m² for obesity in these populations.

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Sex & Age Differences — Women tend to have higher body fat at the same BMI as men. Children and teens require age- and sex-specific percentile charts, not adult cutoffs.

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Pregnancy — BMI is not meaningful during pregnancy as weight gain is expected and healthy. Pre-pregnancy BMI may be used as a reference point for gestational weight gain recommendations.

For a deeper dive into the science and controversy surrounding BMI, the Wikipedia section on BMI limitations and this New England Journal of Medicine perspective on BMI and obesity offer balanced, evidence-based perspectives.

如何达到并保持健康的体重指数

Whether your goal is to lower an elevated BMI or build mass from an underweight baseline, sustainable lifestyle changes consistently outperform short-term diets. Key evidence-based strategies include:

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均衡营养

Focus on whole foods, adequate protein (1.6–2.2 g/kg body weight for muscle retention), and a moderate caloric deficit or surplus. Use our 卡路里计算器 to find your target intake.

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定期体力活动

The WHO recommends at least 150–300 minutes of moderate-intensity aerobic activity per week, plus muscle-strengthening exercises on 2+ days. Check our 每日总能量消耗计算器 to plan your energy expenditure.

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优质睡眠

Chronic sleep deprivation elevates hunger hormones (ghrelin) and suppresses satiety signals (leptin), making weight management significantly harder. Aim for 7–9 hours per night.

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压力管理

Sustained high cortisol promotes fat accumulation—particularly visceral abdominal fat—independent of caloric intake. Mindfulness, yoga, and adequate social support all help.

Combining BMI tracking with complementary tools gives a fuller picture of your health trajectory. We recommend also monitoring your Basal Metabolic Rate (BMR), body fat percentage, and ideal weight range to set realistic, personalised goals.

关于体重指数的常见问题

BMI 25 危险吗？

A BMI of exactly 25 kg/m² sits at the boundary between "healthy weight" and "overweight" categories. By itself, this value is not dangerous, but it signals the point at which statistical health risk begins to increase. Context matters enormously: waist circumference, blood pressure, blood glucose, and cholesterol levels paint a more complete picture than BMI alone.

女性与男性的健康体重指数是多少？

The WHO applies the same BMI cutoffs (18.5–24.9 for healthy weight) to both sexes. However, at any given BMI, women typically carry 5–10% more body fat than men due to hormonal and reproductive factors. This is physiologically normal and does not inherently imply elevated health risk.

我可以拥有健康的体重指数但仍然不健康吗？

Yes. The concept of "metabolically obese, normal weight" (MONW) describes individuals with a normal BMI who carry excess visceral fat and have metabolic risk factors such as insulin resistance, dyslipidemia, or hypertension. Conversely, some individuals with a BMI just above 25 are metabolically healthy. This underscores the importance of comprehensive health assessments beyond BMI alone.

我应该多久检查一次我的体重指数？

For most adults, checking BMI every 3–6 months is sufficient to track meaningful trends. Daily fluctuations in body weight (due to hydration, meals, clothing) can mask true changes, so tracking weekly averages is more informative than single readings.

什么是 BMI Prime？它为何有用？

BMI Prime is your BMI divided by 25 (the upper limit of normal). A value of 1.00 means you are exactly at the boundary; values below 1.00 indicate healthy or underweight status, while values above 1.00 indicate overweight or obesity. BMI Prime is particularly useful for communicating deviation from the healthy range in a simple, percentage-based format.

Related Health Calculators

Tracking your BMI alongside other health metrics provides a comprehensive view of your overall wellbeing. Explore our suite of free health tools:

References & Further Reading

World Health Organization. Obesity and Overweight Fact Sheet. WHO, 2024.
Centers for Disease Control and Prevention. About Body Mass Index. CDC, 2024.
Wikipedia contributors. Body Mass Index. Wikipedia, The Free Encyclopedia.
Wikipedia contributors. Obesity — Health Effects and Epidemiology. Wikipedia, The Free Encyclopedia.
Flegal KM, et al. Association of All-Cause Mortality with Overweight and Obesity Using Standard BMI Categories. JAMA, 2013.
Nuttall FQ. Body Mass Index: Obesity, BMI, and Health — A Critical Review. Nutrition Today, 2015.
WHO Expert Consultation. Appropriate body-mass index for Asian populations. The Lancet, 2004.