BMI Calculator Guide: How Body Mass Index Works
BMI (Body Mass Index) is the most widely used screening tool for weight categories. It takes just two measurements — your height and weight — and produces a single number that estimates body fatness for most adults. This guide explains the formula, how to interpret your result, and where BMI can mislead you.
The BMI Formula
- BMI — body mass index (kg/m²)
- weight — body weight in kilograms
- height — height in meters
For imperial units: BMI = 703 × weight (lb) ÷ height (in)²
For example, a person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9, which falls in the healthy range.
What Your BMI Number Means
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
When BMI Gets It Wrong
- Athletes & bodybuilders — muscle is denser than fat, so muscular people often score "overweight" despite low body fat.
- Older adults — BMI doesn't account for muscle loss or bone density changes with age.
- Pregnant or breastfeeding women — BMI is not meaningful during these stages.
- Different ethnicities — some populations face health risks at lower BMI thresholds; the WHO suggests a 23 cutoff for Asians.
BMI is a screening tool, not a diagnosis. Pair it with waist circumference and body-fat percentage for a fuller picture.
Put It Into Practice
Enter your height and weight in either metric or imperial units to see your BMI instantly, along with your category and the healthy weight range for your height.
BMI（Body Mass Index）是目前应用最广泛的体重分类筛查工具。它只需两个测量值——身高和体重——就能为大多数成年人估算身体脂肪水平，得出一个单一数值。本指南将解释 BMI 的计算公式、如何解读结果，以及 BMI 在哪些情况下可能产生误导。
BMI 计算公式
- BMI — body mass index（kg/m²）
- weight — 体重，单位：千克
- height — 身高，单位：米
英制单位换算：BMI = 703 × 体重（lb）÷ 身高（in）²
例如，一个体重 70 kg、身高 1.75 m 的人，其 BMI 为 70 ÷（1.75 × 1.75）= 70 ÷ 3.0625 ≈ 22.9，属于 healthy range。
你的 BMI 数值意味着什么
| BMI 范围 | 分类 |
|---|---|
| 低于 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 及以上 | Obese |
当 BMI 不准确时
- 运动员和健身爱好者 — 肌肉密度高于脂肪，因此肌肉发达的人往往被标记为"Overweight"，尽管他们的体脂率很低。
- 老年人 — BMI 不考虑因年龄增长导致的肌肉流失或骨密度变化。
- 孕妇或哺乳期女性 — 在这些阶段，BMI 数值没有实际意义。
- 不同种族人群 — 某些人群在更低的 BMI 阈值下就面临健康风险；WHO 建议亚洲人的 cutoff 值为 23。
BMI 是一种筛查工具，而非诊断手段。将其与腰围和体脂率结合使用，可以获得更全面的评估。
付诸实践
输入你的身高和体重（支持公制或英制单位），即可即时查看你的 BMI 数值、所属分类以及该身高对应的 healthy weight range。
Try the BMI Calculator
Supports both metric (kg/cm) and imperial (lb/in) units.
⚖ Open BMI Calculator →