Estimate body fat with a tape measure
The scale tells you how much you weigh, not what that weight is made of. Two people at 180 lb can look and feel very different, one more muscular, the other carrying more fat. This calculator estimates your body fat percentage from a few tape measurements using the US Navy method, then works out your fat mass and lean body mass.
This estimate is for general information only and is not medical advice. For a precise body composition assessment, see a health professional.
The formulas (measurements in centimeters)
Men: body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Women: body fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
The calculator converts inches for you. Then fat mass = weight × body fat % and lean mass = weight − fat mass.
Worked example: a man, 5 ft 10 in and 180 lb
Neck 15.5 in, waist 36 in.
- Waist − neck: 36 − 15.5 = 20.5 in = 52.07 cm; log₁₀(52.07) ≈ 1.717.
- Height: 70 in = 177.8 cm; log₁₀(177.8) ≈ 2.250.
- Denominator: 1.0324 − 0.19077 × 1.717 + 0.15456 × 2.250 ≈ 1.0527.
- Body fat: 495 ÷ 1.0527 − 450 ≈ 20.2%, in the average range.
- Fat mass: 180 × 20.2% ≈ 36.4 lb; lean mass ≈ 143.6 lb.
Effect of waist size (same man)
| Waist | Body fat | Fat mass | Waist-to-height |
|---|---|---|---|
| 30 in | 7.8% | 14.0 lb | 0.43 |
| 32 in | 12.3% | 22.2 lb | 0.46 |
| 34 in | 16.5% | 29.6 lb | 0.49 |
| 36 in | 20.2% | 36.4 lb | 0.51 |
| 38 in | 23.7% | 42.7 lb | 0.54 |
| 40 in | 26.9% | 48.5 lb | 0.57 |
Every inch on the waist matters: it is the measurement most closely tied to abdominal fat.
Body fat categories
| 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% and above | 32% and above |
These American Council on Exercise ranges are widely used. Essential fat, needed for hormones and nerve function, is naturally higher in women.
Getting reliable measurements
Measure in the morning before eating, standing relaxed, with a flexible tape lying flat on the skin without compressing it. Take each measurement twice. The US Navy method typically lands within 3–4 percentage points of laboratory methods such as DEXA and is most useful for tracking change over weeks under the same conditions.
What next?
A high result, and especially a waist-to-height ratio above 0.5, is worth discussing with your doctor. Regular activity, strength training, enough sleep and a balanced diet reduce body fat more durably than crash diets.