4 Point Body Fat Calculator

Durnin 4-site Formula:

\[ Body\ Density = c - (m \times \log(sum\ of\ 4\ skinfolds)) \] \[ Body\ Fat\% = \left(\frac{4.95}{Body\ Density} - 4.5\right) \times 100 \]

Triceps Skinfold (mm):

Biceps Skinfold (mm):

Subscapular Skinfold (mm):

Iliac Crest Skinfold (mm):

Gender:

Age:

years

Estimated Body Fat Percentage:

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1. What is the Durnin 4-site Formula?

The Durnin 4-site formula is a method for estimating body fat percentage using skinfold measurements at four anatomical sites. It's based on the relationship between subcutaneous fat and total body fat, with age- and gender-specific equations.

2. How Does the Calculator Work?

The calculator uses the Durnin-Womersley equations:

\[ Body\ Density = c - (m \times \log(sum\ of\ 4\ skinfolds)) \] \[ Body\ Fat\% = \left(\frac{4.95}{Body\ Density} - 4.5\right) \times 100 \]

Where:

\( c \) — Age- and gender-specific constant
\( m \) — Age- and gender-specific multiplier
\( sum\ of\ 4\ skinfolds \) — Triceps + Biceps + Subscapular + Iliac crest measurements (mm)

Explanation: The formula first calculates body density from skinfold measurements, then converts this to body fat percentage using the Siri equation.

3. Importance of Body Fat Measurement

Details: Body fat percentage is a key indicator of health and fitness. It helps assess obesity risk, track fitness progress, and guide nutrition and training programs more accurately than BMI alone.

4. Using the Calculator

Tips: Enter skinfold measurements in millimeters (accurate to 0.1mm), select gender and age. All skinfold values must be >0 and age between 16-100 years.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the Durnin 4-site method?
A: It's reasonably accurate (±3-4%) for general population when measurements are taken properly, though less accurate than DEXA or hydrostatic weighing.

Q2: What are healthy body fat percentages?
A: For men: 6-24% (athletes 6-13%, fitness 14-17%, average 18-24%). For women: 16-30% (athletes 14-20%, fitness 21-24%, average 25-30%).

Q3: Where exactly are the measurement sites?
A: Triceps: back of upper arm midway; Biceps: front of upper arm midway; Subscapular: diagonal fold below shoulder blade; Iliac crest: diagonal fold above hip bone.

Q4: Who shouldn't use this method?
A: Not suitable for those with very high or very low body fat, pregnant women, or people with significant edema or skin conditions.

Q5: How can I improve measurement accuracy?
A: Use proper calipers, take measurements on right side of body, ensure consistent pressure, measure multiple times and average, have same technician take all measurements.