Body Fat % Calculator (Jackson-Pollock)
The Jackson-Pollock 3-site skinfold method is one of the most validated field tests for estimating body fat percentage. By measuring subcutaneous fat at three specific sites with calipers, it predicts body density via a sex-specific regression equation, then converts that density to body fat % using the Siri formula. Results include lean mass, fat mass, and an ACE-based classification.
When to use this calculator
- Tracking body composition changes during a cut or bulk
- Baseline fitness assessment before starting a new training program
- Comparing body fat levels against ACE health classification standards
- Estimating lean body mass to calculate protein targets
- Monitoring fat loss progress more accurately than scale weight alone
- Pre-competition body composition check for athletes
How it works
2 min readWhat is the Jackson-Pollock 3-site method?
The Jackson-Pollock 3-site method estimates body fat percentage by measuring skinfold thickness at the chest, abdomen, and thigh using calipers. These measurements are plugged into a sex-specific regression equation to calculate body density, which then converts to body fat percentage. It's one of the most validated field assessment techniques in fitness science.
How It Works
The Jackson-Pollock method uses sex-specific polynomial regression equations fitted to a large population sample (Jackson & Pollock, 1978 for men; Jackson, Pollock & Ward, 1980 for women). The sum of three skinfold measurements (S) and age (A) predict body density (Db), which is then converted to body fat % with the Siri (1956) equation.
Formula
// Men (chest + abdominal + thigh)
S = skinfold1 + skinfold2 + skinfold3 (mm)
Db = 1.10938 - (0.0008267 × S) + (0.0000016 × S²) - (0.0002574 × Age)
// Women (triceps + suprailiac + thigh)
Db = 1.0994921 - (0.0009929 × S) + (0.0000023 × S²) - (0.0001392 × Age)
// Siri equation (body fat %)
Body Fat % = ((4.95 / Db) - 4.50) × 100
// Mass partitioning
Fat Mass = Total Weight × (Body Fat % / 100)
Lean Mass = Total Weight - Fat MassWorked Example
| Variable | Value |
|---|---|
| Sex | Male |
| Age | 35 years |
| Chest skinfold | 15 mm |
| Abdominal skinfold | 20 mm |
| Thigh skinfold | 18 mm |
| S (sum) | 53 mm |
| Body density | 1.0647 g/mL |
| Body Fat % | 17.2% |
| Weight | 175 lb |
| Fat Mass | 30.1 lb |
| Lean Mass | 144.9 lb |
ACE Body Fat Classification (2026)
| 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% |
Limitations
Frequently asked questions
What sites do I measure for men vs. women?
Men use chest, abdominal, and thigh. Women use triceps, suprailiac (just above the hip bone), and thigh. Measuring the wrong sites invalidates the result.
How do I measure a skinfold correctly?
Pinch a fold of skin plus subcutaneous fat (not muscle) between thumb and index finger, apply caliper jaws 1 cm away from the pinch, release the caliper lever, and read after 2 seconds. Take three readings and average them.
How accurate is the Jackson-Pollock method?
With a trained tester, the standard error of estimate (SEE) is approximately ±3.5% body fat compared to hydrostatic weighing. DEXA typically has an SEE of ±1.5–2%. JP3 is practical and inexpensive for tracking trends.
What is the Siri equation?
Siri (1956) derived Body Fat % = ((4.95 / Db) − 4.50) × 100, assuming a two-compartment model where fat density ≈ 0.9 g/mL and fat-free mass density ≈ 1.1 g/mL.
Can I use this for people over 65?
The original equations were validated on adults aged 18–61. Older adults tend to have more intra-muscular and visceral fat not captured by skinfolds, so results may underestimate true body fat. Use with caution.
What does 'lean mass' include?
Lean body mass (LBM) is everything except fat: muscle, bone, organs, water, and connective tissue. It is NOT the same as muscle mass alone.
What is 'essential fat'?
Essential fat is the minimum needed for physiological function: bone marrow, organs, and the central nervous system. For men it's ~2–5%; for women ~10–13% (higher due to sex-specific hormonal fat).
How often should I measure?
Every 4–8 weeks is sufficient for tracking changes. More frequent measurement adds noise without meaningful signal, given natural day-to-day hydration variation.
Why does my result differ from a bioimpedance scale?
Bioimpedance (BIA) is highly sensitive to hydration, meal timing, and electrode placement. JP skinfolds and BIA use different models; discrepancies of 2–5% are common and expected.
Is a lower body fat % always better?
No. Going below essential fat thresholds is dangerous. Athletes benefit from low body fat, but extreme leanness can impair hormone function, immunity, and bone density, especially in women (Female Athlete Triad).
Sources and references
- Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr. 1978;40(3):497–504.
- Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc. 1980;12(3):175–181.
- Siri WE. Body composition from fluid spaces and density: analysis of methods. Techniques for Measuring Body Composition. 1956.
- American Council on Exercise — Percent Body Fat Norms
- NIH Body Weight Planner & Body Composition Background