Nutrition
How to measure your body fat percentage: methods and a skinfold guide
The methods for measuring body fat, how accurate each one is, and how to measure skinfolds step by step, with sites, equations, and reference ranges.
Weight doesn't tell you what a change is made of. Two people with the same weight and height can be at 15% or 30% body fat. Measuring body fat percentage tells you whether a client is losing fat or muscle, so you can adjust the plan in time.
There is no perfect method: each one trades off accuracy, cost, and convenience. What you can control is measuring the same way every time.
The methods available
| Method | How it works | Approximate error | When to use it |
|---|---|---|---|
| DEXA | Low-dose X-rays that separate fat, muscle, and bone | ±1-2 points | Clinical and research reference; expensive and hard to access |
| Hydrostatic weighing or air displacement (Bod Pod) | Measure body density | ±2-3 points | Laboratory; rarely in practice |
| Skinfolds | Caliper at standard sites plus an equation | ±3-4 points, measured well | The most practical option in clinic |
| Bioimpedance | A weak current estimates body water and lean mass | ±3-5 points, sensitive to hydration | Quick, if you control the conditions |
| Girths (US Navy formula) | Waist, neck, and hip | ±3-4 points | When you have no caliper |
| BMI | Weight divided by height squared | Does not measure fat | Population screening, not body composition |
Why skinfolds are the most practical option in clinic
A good caliper is inexpensive, the measurement takes 5 to 10 minutes and, with a standardized technique, it is consistently repeatable. The sum of skinfolds in millimeters is also useful on its own: if it drops, the client lost subcutaneous fat, whichever equation you use.
What you need
- A calibrated constant-pressure caliper (Harpenden, Lange, or similar, at 10 g/mm²).
- A tape measure to locate the sites.
- A skin marker to mark them.
- A spreadsheet or software to record each measurement.
How to measure skinfolds, step by step
- Measure with the client standing, relaxed, and with dry skin. Avoid measuring right after training or a hot shower.
- Always use the right side of the body.
- Locate and mark each site with the tape measure before measuring.
- Grasp the fold between thumb and index finger, about 8 cm apart, lifting skin and fat but not muscle.
- Place the caliper 1 cm below your fingers, halfway up the fold, without letting go of the fold.
- Read the value 1 or 2 seconds after releasing the caliper jaws.
- Measure each site 2 or 3 times, rotating between sites. If two readings differ by more than 2 mm, repeat. Use the average.
- Write down the values in millimeters and apply the equation.
Where to measure each skinfold
| Site | Direction | Location |
|---|---|---|
| Chest | Diagonal | Halfway between the anterior axillary line and the nipple (in women, one third of the way from the armpit) |
| Midaxillary | Vertical | Midaxillary line, at the level of the xiphoid process |
| Triceps | Vertical | Back of the arm, halfway between the acromion and the olecranon |
| Biceps | Vertical | Front of the arm, at the level of the triceps skinfold |
| Subscapular | Diagonal (45°) | 1-2 cm below the inferior angle of the scapula |
| Abdominal | Vertical | To the right of the navel: 2 cm for Jackson-Pollock, 5 cm in the ISAK protocol |
| Suprailiac | Diagonal | Just above the iliac crest, on the anterior axillary line |
| Supraspinale | Oblique | Where the line from the anterior superior iliac spine to the anterior axillary border crosses the level of the iliac crest |
| Thigh | Vertical | Front of the thigh, halfway between the inguinal crease and the kneecap |
| Calf | Vertical | Inner side, at the widest girth |
Which equation to use
- Jackson-Pollock 3-site: chest, abdomen, and thigh in men; triceps, suprailiac, and thigh in women. The quickest, validated in men aged 18 to 61 and women aged 18 to 55.
- Jackson-Pollock 7-site: chest, midaxillary, triceps, subscapular, abdomen, suprailiac, and thigh. More stable when fat is distributed unevenly.
- Durnin-Womersley: biceps, triceps, subscapular, and suprailiac, with one equation per age band (16 to 72 years). Useful when measuring the abdomen or thigh is impractical.
- Yuhasz: the sum of the 6 ISAK skinfolds (triceps, subscapular, supraspinale, abdominal, thigh, and calf). Widely used in sport.
Jackson-Pollock and Durnin-Womersley estimate body density, which the Siri equation (the most common) or the Brozek equation then turns into body fat percentage. Yuhasz returns the percentage directly.
How to read the result
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| High | 25% or more | 32% or more |
These ranges are a guide, not a diagnosis: read them alongside the client's age, clinical context, and goal. Women carry more essential fat for hormonal and reproductive reasons, which is why their ranges are higher.
How often to measure
Every 4 to 8 weeks is enough. Sooner than that, the real change is usually smaller than the measurement error. Record the sum of skinfolds and girths too: if the sum drops while weight holds steady, body recomposition is likely.
Common mistakes
- Switching assessor, caliper, or equation between visits.
- Measuring over clothing, on damp skin, or over lotion.
- Pinching muscle along with fat, especially on the thigh.
- Reading the caliper too late: the fat compresses and the value drops.
- Comparing a skinfold result with a bioimpedance scale reading.
- Using skinfolds in severe obesity: the fold can exceed the caliper's opening and the technique loses accuracy. Girths or bioimpedance work better there.
Frequently asked questions
Can I measure my own body fat with skinfolds?
It's hard: sites such as the triceps or subscapular are difficult to reach with one hand. For a reliable result, have a trained professional measure you, and keep it the same person each time.
How accurate is the skinfold method?
Measured well, skinfolds land about 3-4 points from reference methods. Their main strength is tracking change in the same person with the same assessor.
Is bioimpedance better than skinfolds?
Not necessarily. Bioimpedance is quicker but varies with hydration, meals, and recent exercise. Both work if you keep the same conditions at every measurement.
About the author
Equipo Almendra
Editorial · Almendra
The Almendra editorial team brings together nutritionists, engineers, and product managers writing about how to run a modern nutrition practice.
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