There is no way to measure body fat at home that is both perfectly accurate and free. The question is which method is accurate enough for what you want to do. If your goal is to track progress over months, consistency matters more than precision. If you need a reference number for a clinical or sports reason, a lab-based method is more appropriate.
The methods at a glance
| Method | How it works | Typical accuracy | Cost and effort | Best for |
|---|---|---|---|---|
| DEXA scan | Low-dose X-rays separate fat, lean and bone | Often within about 2 to 3 percentage points; affected by hydration and the machine | Clinic or gym visit; fee varies | Detailed regional and bone data |
| Hydrostatic weighing | Weight underwater vs on land gives body density | Within about 2 to 3 points if done well | Lab; needs full submersion and exhaling | Reference-style single measurement |
| Air displacement (Bod Pod) | Measures body volume by air displacement | Similar to hydrostatic weighing | Lab or gym | Comfortable alternative to water |
| Skinfold calipers | Pinch thickness at 3 to 7 sites into an equation | Within 3 to 5 points in skilled hands; worse with poor technique | Cheap tool; needs practice | Trend tracking with the same tester |
| Bioimpedance (smart scales, handhelds) | Small current measures resistance; lean tissue conducts better | Absolute error often 3 to 8 points; varies with hydration | Cheap; convenient | Day-to-day trend, with controlled conditions |
| US Navy tape method | Neck, waist (and hip for women) plus height in a formula | Often within 3 to 4 points on average; larger individual error | Free with a tape measure | Home estimate and trend |
| BMI-based equations | Estimate from BMI, age and sex | Rough; ignores muscle | Free | Quick sanity check only |
| Photo estimate | Estimates circumferences from a photo, then a formula | Rougher than tape | Free, phone only | Visual tracking and convenience |
Numbers are typical and vary by study, device and population. If you see a claim of "99% accurate", be sceptical.
DEXA
Dual-energy X-ray absorptiometry was designed to measure bone density but it also reports fat and lean mass by region. It is widely considered the most practical high-detail method. Strengths: repeatable, regional data, low radiation. Weaknesses: results depend on hydration and the specific machine and software, so DEXAs on different devices are not directly comparable; access and cost.
Hydrostatic weighing and Bod Pod
Both estimate body density, and then use a formula to convert density to fat percentage. They rely on assumptions (about the density of lean tissue) that do not hold for everyone: older adults, some ethnic groups, and people with unusual bone density can be misjudged.
Skinfold calipers
A skilled tester pinches subcutaneous fat at fixed sites (for example, chest, abdomen and thigh in the Jackson-Pollock 3-site method for men) and puts the sum into an equation. Errors come from site selection, pinch pressure and equation choice. Self-testing is difficult. If you use calipers, use the same sites, the same person and the same time of day.
Bioimpedance scales
These pass a tiny current through your body and use its resistance to estimate water and, from that, lean mass. Being well hydrated makes you look leaner; being dehydrated makes you look fatter. Exercise, meals, alcohol and even the time of day change the reading. For tracking, weigh under the same conditions (morning, before eating) and watch the four-week trend, not the daily figure.
US Navy tape method
Developed by the US Navy in the 1980s (Hodgdon and Beckett) as a way to screen recruits without special equipment, it uses height, neck and waist, plus hips for women, in a formula based on logarithms:
- Men: 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
- Women: 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
Measurements are in centimetres. The method does well for typical builds and worse for very muscular or very lean people. Because it relies on your waist and neck, it responds well to real changes in waist size, which is what most people are trying to change.
Photo-based estimates
A photo can be used to estimate widths and, with a depth estimate from a side photo, circumferences, which then feed the Navy formula. It is convenient but less accurate than a tape, because clothing, posture, lens distortion and landmark placement all add error. On this site, when tape measurements and photo estimates are both available, tape wins.
How to choose
- You want to track progress at home: Use a tape measure for waist, plus the Navy estimate, plus monthly photos. See how to measure your body and progress tracking.
- You want a single reference measurement: a DEXA or Bod Pod, ideally at the same facility for repeats.
- You are curious and want low effort: a smart scale, weighing under controlled conditions, interpreting the trend only.
- You have a medical reason: ask a clinician which measure is appropriate.
Rules for any method
- Use the same method, at the same time of day, under the same conditions each time.
- Ignore changes smaller than about 2 percentage points; they are likely noise.
- Compare with waist size, strength, photos and how your clothes fit.
- Do not compare numbers across methods.
Reference ranges for interpreting your result are on the body fat percentage chart.