3-Point Skin Fold Bodyfat
Estimate body fat percentage and lean body mass from your age, weight, and pectoral, abdominal, and thigh skinfold measurements. Enter each skinfold thickness in millimeters.
Jackson-Pollock Skinfold Calculator
3-Point Body Fat Formula
Where:
- \(P\), \(A\), and \(T\) — pectoral, abdominal, and thigh skinfold thicknesses (mm)
- \(S\) — sum of the three skinfolds (mm)
- \(a\) — age (years)
- \(D\) — estimated body density (g/cm³)
- \(F\) — estimated body fat percentage (%)
- \(W\) — body weight (kg or lb); \(L\) — lean body mass in the same unit
The calculator estimates body density from the skinfold sum and age, then converts density to body fat percentage using the Siri equation. Lean body mass is body weight minus estimated fat mass.
3-Point Body Fat – Calculation Example
Example: a 25-year-old man weighs 70 kg. His pectoral, abdominal, and thigh skinfolds measure 12 mm, 20 mm, and 18 mm.
\[S=12+20+18=50\text{ mm}\]
\[D=1.10938-0.0008267(50)+0.0000016(50)^2-0.0002574(25)=1.06561\]
\[F=\frac{495}{1.06561}-450\approx14.52\%\]
\[L=70\left(1-\frac{14.52}{100}\right)\approx59.83\text{ kg}\]
Result: approximately 14.52% body fat and 59.83 kg of lean body mass. The lean-mass result uses the unrounded body fat estimate.
How to use the calculator
- Choose Unit system: Metric for a weight in kilograms or English for a weight in pounds. Skinfold measurements remain in millimeters either way.
- Select Gender (Men or Women) to choose the corresponding body-density equation.
- Enter your Age in years and Weight in the unit you selected.
- Use skinfold calipers to measure your Pectoral fold, Abdominal fold, and Thigh fold. Enter each measurement in millimeters.
- Read Body Fat Percentage and Lean Body Mass in the results. Lean body mass is shown in kilograms for Metric or pounds for English.
What a 3-point skinfold result means
A skinfold caliper measures the thickness of a pinch of skin and underlying fat. This calculator adds three measurements, uses the sum and your age to estimate body density, and converts that density into an estimated body fat percentage. For example, a result of 14.52% means the method estimates that about 14.52% of total body weight is fat. It is an estimate, not a direct measurement of all body fat.
Lean body mass is everything other than estimated fat mass, including muscle, bone, organs, and water. It is not the same as muscle mass. Because the lean-mass calculation uses your body fat estimate, any error in the skinfold measurements also affects the lean-mass result. If you want to use that estimate in an energy-needs calculation, see the Katch-McArdle BMR calculator.
Repeated measurements can help you observe a trend, particularly when the same person measures the same sites with the same calipers. A small change in the displayed percentage may reflect measurement variation rather than a real change in body composition. For a different approach, compare results with a circumference-based body fat calculator or explore other methods with the body fat calculator.
Measurement tips and limitations
Measure on the same side of the body each time and follow a consistent anatomical-site protocol. Grasp the skinfold firmly, place the caliper jaws beside your fingers rather than on them, and read the caliper after its pressure has settled. Take several readings at each site and use a consistent summary, such as their average. Avoid measuring immediately after exercise, when shifts in fluid and blood flow may affect readings.
Important for women: this calculator applies the women’s equation to the pectoral, abdominal, and thigh fields. The commonly published Jackson–Pollock three-site protocol for women instead uses triceps, suprailiac, and thigh measurements. Those sites are not interchangeable. As a result, the women’s output here should not be treated as a validated estimate from the standard women’s three-site protocol; use a tool with the correct site fields if you need that method.
Skinfold equations and the body-density conversion rely on population-based assumptions. Results can vary with the measurer’s technique, caliper quality, fat distribution, and individual body composition. The form accepts ages from 10 years, but these adult-oriented equations should not be relied on for children or adolescents. The English setting changes the lean-mass unit shown; it does not convert the number entered for Weight, so enter pounds when using English even if the field still displays “kg.”
Frequently Asked Questions
Where exactly should I measure the three skinfolds?
Use a consistent anatomical protocol for all three sites. The pectoral fold is typically a diagonal pinch between the front of the armpit and the nipple; the abdominal fold is a vertical pinch about 2 cm to the right of the navel; and the thigh fold is a vertical pinch midway between the hip crease and the top of the kneecap. These locations do not replace the standard women’s three-site protocol.
What is a healthy body fat percentage?
There is no single healthy percentage for everyone. Body fat varies with age, sex, and individual health, and a skinfold estimate is not precise enough to diagnose whether someone has too much or too little body fat. Consider the result alongside your health history and other measures. If you are concerned about a very low or high result, speak with a qualified healthcare professional.
Can I enter skinfold measurements in inches?
No. Convert each skinfold reading to millimeters before entering it: multiply inches by 25.4. For example, 0.5 inch is 12.7 mm. This conversion applies even when you select English for body weight; that setting only changes the weight unit. Mixing inches and millimeters will substantially distort the body fat estimate.
Why does the calculator show an implausible result for very small or very large folds?
The equations are estimates, not physical limits on body fat. Zero or extreme skinfold entries can produce percentages that are not plausible, because the equation is being used outside a useful measurement range. Check for missing readings, unit mistakes, and caliper placement. Do not interpret an implausible output as a real body-composition measurement.
How often should I measure skinfolds to track progress?
Measuring every few weeks is usually more informative than reacting to day-to-day changes. Use the same sites, calipers, measurer, and measurement conditions each time, and compare longer-term patterns. A small change in one result may come from differences in how the fold was pinched or read rather than a change in body fat.
Why is my skinfold result different from a DEXA scan or smart scale?
Each method measures or estimates body composition differently. Skinfolds use subcutaneous fat thickness and a population-based equation; smart scales typically infer composition from electrical impedance, while DEXA uses X-ray measurements. Hydration, measurement technique, and individual fat distribution can widen the differences. Avoid treating the methods as interchangeable when tracking change, and ask a healthcare professional if a result will guide a medical decision.