Body Fat Calculator — Complete Guide
The scale cannot tell you what you are made of. Two people at the same height and weight can carry very different amounts of fat, which is why body fat percentage — not body weight — is the number that describes composition. This calculator estimates it with the method the US Navy has used for decades: a tape measure and a formula.
What this calculator does
Enter your height, weight, neck and waist — plus hip circumference if female — in centimetres/kilograms or inches/pounds. The tool returns your estimated body fat percentage, splits your weight into fat mass and lean mass, places the result in a category from essential fat to obese, and shows your BMI for comparison.
The method
men: BF% = 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
women: BF% = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450
All measurements are in inches. The logic is geometric: fat accumulates around the waist, muscle does not, so a larger waist relative to neck and height implies more fat. The formula was published by Hodgdon and Beckett (1984) and validated against hydrostatic weighing on Navy personnel.
A worked example
A man 175 cm tall with a 38 cm neck and an 85 cm waist: converted to inches that is 68.9, 15.0 and 33.5. BF% = 495 ÷ (1.0324 − 0.19077·log₁₀(18.5) + 0.15456·log₁₀(68.9)) − 450 ≈ 10.6%. At 70 kg that is about 7.4 kg of fat mass and 62.6 kg of lean mass — the "athletes" band for a man, which shows how demanding the Navy table is: a waist of 85 cm at this height is already lean by its standard.
| Category | Men | Women |
|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
How to measure well, and what to expect
- Measure in the morning, before eating, with the tape level against the skin — snug but not compressing.
- Neck: just below the larynx, slightly forward-tilted. Waist: at the navel for men, at the narrowest point for women. Hip: the widest point of the glutes.
- Expect ±3–4 points of error against a DEXA scan — treat the number as a trend line, not a verdict. Measuring monthly under the same conditions is far more informative than any single reading.
- Losing fat while gaining muscle may leave your body fat falling while BMI stays flat — which is exactly why the two numbers are shown together.
Body fat percentage is one of several lenses on health, alongside waist-to-height ratio, blood pressure and fitness markers. Use it to set a direction; use your doctor's tools to set the diagnosis.
体脂率计算器完整使用指南
体重秤看不出你的身体构成。两个身高体重完全相同的人，脂肪含量可能差别很大——所以描述身材的关键数字是体脂率，而不是体重。这个计算器用美国海军沿用几十年的方法估算体脂：一把皮尺加一条公式。
这个计算器能做什么
输入身高、体重、颈围、腰围（女性再加臀围），支持公制（厘米/公斤）和英制（英寸/磅）。工具会给出估算体脂率，把体重拆分为脂肪量与瘦体重，按从「必需脂肪」到「肥胖」的区间给出分类，并附上 BMI 供对照。
计算方法
男性：体脂率 = 495 ÷ (1.0324 − 0.19077·log₁₀(腰围 − 颈围) + 0.15456·log₁₀(身高)) − 450
女性：体脂率 = 495 ÷ (1.29579 − 0.35004·log₁₀(腰围 + 臀围 − 颈围) + 0.22100·log₁₀(身高)) − 450
公式中所有围度以英寸计。背后的逻辑是几何性的：脂肪倾向堆积在腰腹部，而肌肉不会，因此腰围相对颈围和身高越大，体脂就越高。该公式由 Hodgdon 与 Beckett 于 1984 年发表，并在海军人员身上与水下称重法做了对照验证。
算例演示
男性，身高 175 厘米、颈围 38 厘米、腰围 85 厘米：换算成英寸分别为 68.9、15.0、33.5。体脂率 = 495 ÷ (1.0324 − 0.19077·log₁₀(18.5) + 0.15456·log₁₀(68.9)) − 450 ≈ 10.6%。按 70 公斤计，脂肪量约 7.4 公斤、瘦体重约 62.6 公斤——已进入男性「运动员水平」区间，可见海军标准相当严格：这个身高下 85 厘米的腰围在它眼里已经算精瘦。
| 分类 | 男性 | 女性 |
|---|
| 必需脂肪 | 2–5% | 10–13% |
| 运动员水平 | 6–13% | 14–20% |
| 健康水平 | 14–17% | 21–24% |
| 普通水平 | 18–24% | 25–31% |
| 肥胖 | 25% 以上 | 32% 以上 |
怎么测得更准、结果怎么看待
- 早晨空腹测量，皮尺水平贴合皮肤——贴紧但不压迫。
- 颈围：喉结下方、头稍前倾；腰围：男性过肚脐、女性取最细处；臀围：臀部最宽处。
- 与 DEXA 扫描相比误差约 ±3–4 个百分点——把它当趋势线而不是判决书。每月在相同条件下测一次，远比任何单次数值更有价值。
- 减脂同时增肌时，可能出现体脂率下降而 BMI 纹丝不动——这正是两个数字要放在一起看的原因。
体脂率只是观察健康的镜头之一，和腰高比、血压、体能指标放在一起才完整。用它定方向，诊断请交给医生的工具。