Jackson–Pollock Skinfolds for Women Over 40 — What This Calculator Estimates

A skinfold test measures the thickness of subcutaneous fat using calipers at specific sites on the body. These measurements estimate body density using the Jackson–Pollock formula, which is then converted to body fat percentage using the Siri equation.

Unlike the numbers that you see on the scale, body fat percentage shows how much of your weight is fat versus muscle. This matters even more during perimenopause and postmenopause, when hormonal shifts can increase fat storage and accelerate muscle loss.

Skinfold testing follows standardized formulas created specifically for women. Both the 3-site and 7-site Jackson–Pollock methods use the same calculation principles but differ in the number of measurement locations. The 3-site method is faster and easier to repeat at home, making it ideal for beginners. The 7-site method includes more areas of the body and captures changes in fat distribution.

Neither is more accurate than the other. The best method is the one that you can perform consistently.

The calculator provides lean body mass, a key number for setting protein targets, understanding metabolism, and tracking strength progress over time.

Choose Your Test: 3-Site vs 7-Site (Female Protocols)

3-Site (Female) : Speed/Consistency at Home

The 3-site method measures three major fat storage areas commonly affected by hormonal changes:

• Triceps: reflects fat in the upper arm
• Suprailiac: measures fat near the waist
• Thigh: captures lower-body fat

These sites are easy to reach and repeat accurately. Because fewer measurements reduce user error, the 3-site method is often the most reliable for home use. It’s best for beginners, solo measurement, and consistent tracking.

7-Site (Female): More Detail if You’re Experienced

The 7-site method adds four additional locations to give a fuller picture of fat distribution:

• Chest (diagonal)
• Mid-axillary (side of torso)
• Subscapular (below shoulder blade)
• Abdomen (vertical near navel)

While not necessarily better, it does detect changes in the upper body, which can increase during menopause as estrogen levels decline. However, measuring more areas means that you’re more prone to making user errors. Not to mention, you’ll need someone’s help with harder-to-reach areas. But it’s worth it to do the 7-site method if you want to highlight subtle changes that the 3-site method might miss.

Because of the added layer of complication, the 7-site method is best for experienced users, detailed analysis, and spotting fat distribution patterns.

How to Take Each Skinfold (Quick How-To)

Proper technique matters. Skinfold testing measures the layer of fat just under the skin. This is why consistency in how you pinch and read each site is important. The same method, same person, and same conditions matter more than getting the “perfect” number.

We recommend always measuring on the right side of the body, because that’s how the original formulas were validated. Use your fingers to lift the skin and fat away from the muscle, then place the caliper about 1 cm below your fingers. Wait 1–2 seconds before reading so the tension stabilizes. Rotate through each site and repeat 3 readings per site, then average them to reduce variability.

General Rules

Set yourself up the same way each time to improve reliability:

• Test in the morning, before workouts or meals
• Stay hydrated, but avoid testing after salty food or alcohol
• Relax the area being measured—muscle tension skews results
• Pinch firmly to separate fat from muscle
• Apply the caliper at the correct angle (vertical or diagonal, depending on site)
• Wait 1–2 seconds before reading
• Record three measurements and only average readings within 2 mm of each other

Site Cues

Triceps (Vertical)

‍Midpoint between acromion & olecranon, back of arm

Let the arm hang naturally. Locate the shoulder bone (acromion) and elbow bone (olecranon). Measure halfway between them on the back of the arm. Pinch a vertical fold. This area often changes with hormonal shifts or strength training progress.

Tip: If the fold is hard to grasp, relax the arm more or have someone assist.

Suprailiac (Diagonal)

Just above iliac crest along natural angle, anterior axillary line

Find the top of the hip bone (iliac crest), then move slightly forward toward the armpit (anterior axillary line). Pinch along the natural diagonal angle of the skin. This site reflects fat stored around the waist, which often increases during perimenopause due to changes in estrogen and cortisol.

Thigh (Vertical)

‍Midline front thigh, halfway hip crease → patella

Stand with most of your weight on the opposite leg or place your foot on a chair to relax the thigh. Find the midpoint between the hip crease and kneecap, then pinch a vertical fold on the front of the thigh. This fold is thicker, so use your whole hand.

For accuracy, avoid measuring this area after doing leg workouts, long walks, or heat exposure.

7-Sites Adds

If you’re using the 7-site method, four additional locations give you better insight into how fat is distributed throughout your body.

• Chest (diagonal): Halfway between armpit and nipple. Useful for spotting upper body fat shifts from strength training or hormonal changes.

• Mid-axillary (vertical): Vertical fold on the side of the torso at the level of the sternum. Reflects side torso fat.

• Subscapular (diagonal): Just below the shoulder blade at a diagonal angle. Often increases with age-related fat redistribution.

• Abdomen (vertical): One inch next to the belly button. Tracks central fat, which is linked to metabolic risk.

The Math Behind the Tool (Shown Transparently)

Here’s what actually happens when you enter your data:

1. Each skinfold measurement (in millimeters) is added together.
2. That total goes into the Jackson–Pollock equation to estimate body density.
3. The Siri equation converts body density into body fat percentage.
4. Lean body mass (LBM) is calculated from your body fat % and weight.

While no field method is perfect, research shows that skinfold testing is a more reliable method of tracking trends.

Sum Your Skinfolds (mm) → Jackson–Pollock Body Density (Db)

The calculator uses different formulas depending on the method you choose:

Women, 3-site: Db = 1.0994921 − 0.0009929·Σ3 + 0.0000023·(Σ3²) − 0.0001392·Age

Women, 7-site: Db = 1.097 − 0.00046971·Σ7 + 0.00000056·(Σ7²) − 0.00012828·Age

Age matters because skin elasticity and fat distribution change over time, and body density decreases even at similar skinfold sums. But the relationship between fat and density isn’t perfectly linear. It’s a term that improves accuracy in people with higher fat levels.

Convert Db → Body Fat % (Siri)

• %Fat = (495 / Db) − 450

The Siri equation is a standard in exercise physiology. It assumes fat mass and lean mass have consistent densities across individuals.

Strengths

• Works well for most healthy adults
• Consistent and predictable
• Ideal for tracking trends over time

Limitations

• May slightly overestimate in very lean individuals

As long as the same equation is used every time, the direction of change (up or down) will remain accurate.

Get Lean Body Mass

• LBM = Body Weight × (1 − Body Fat%)

Lean body mass (LBM) includes muscle, bone, organs, and water. It’s a number that reflects how much metabolically active tissue you have. During perimenopause and postmenopause, estrogen declines accelerate muscle loss and slow metabolism if protein intake and strength training are low. Finding your LBM helps you personalize nutrition instead of using generic calorie charts.

LBM is the anchor for setting protein, calories, and strength goals. It’s what shows whether your workouts are preserving muscle, which the scale can’t tell you.

Use Your Results — Protein, Macros, and Progress

Knowing your body fat percentage helps, but what you do with that number is what matters the most.

Once you know your LBM, you can target your protein intake accurately, choose the right calorie range, and track progress based on your body composition. This is especially important in your 40s. You might see changes in your body, as your body fat rises and your muscle percentage drops, even though you weigh the same as before.

Using this calculator can help tell you if your plan is working, without obsessing over the scale.

Set protein from LBM

Research shows that higher protein intake supports muscle maintenance, appetite control, and recovery during fat loss. Using LBM makes this even more precise.

Two practical options:

• By total body weight: 1.6–2.2 g per kg
• By LBM: 2.0–2.4 g per kg

Example protein-rich meals:

• Greek yogurt + berries + chia seeds
• Chicken breast with quinoa and veggies
• Tofu stir-fry with edamame
• Cottage cheese with fruit and almonds

Pick a Goal

Your calorie target should match your goa. Paired with strength training, it can help you protect or build muscle.

Here’s a table to help guide you on your goal:

Just a reminder, strength training is non-negotiable. Do it 2-3 times a week. It’s what signals your body to keep building muscle. Without resistance or strength training, most of your weight loss can come from muscle instead of fat.

Accuracy, Re-Testing, and Midlife Notes

Skinfold tests are most valuable when used to track trends. It isn’t meant for single results. Your body changes every day, based on your hydration levels, sodium intake, sleep, stress, and even recent workouts. Hormone fluctuations can also have a huge impact. This is why a single reading is often inaccurate. You need consistent repeat testing to find a reliable pattern based on meaningful data.

To improve accuracy, create a consistent testing routine:

Best Practices

• Test first thing in the morning
• Go to the bathroom first
• Be normally hydrated
• Avoid testing after workouts, sauna, alcohol, or salty meals
• Use the same measurer (or the same hand and technique if doing it yourself)
• Take three readings per site and only average values within 2 mm of each other

How Often to Test

• Every 2–4 weeks is ideal
  • Less than 2 weeks: too much noise
  • More than 4 weeks: you might miss important changes

Sources

1. Kispert CP, Merrifield HH. Interrater reliability of skinfold fat measurements. Phys Ther. 1987;67(6):917-920. doi:10.1093/ptj/67.6.917
2. Kokura, Yoji, et al. "Enhanced Protein Intake on Maintaining Muscle Mass, Strength, and Physical Function in Adults with Overweight/Obesity: A Systematic Review and Meta-analysis." Clinical Nutrition ESPEN, vol. 63, 2024, pp. 417-426, https://doi.org/10.1016/j.clnesp.2024.06.030

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