Sample inputs and outputs to verify your workflow.
| Method | Sex | Age | Inputs (summary) | Density (g/ml) | Body Fat % (Siri) |
|---|---|---|---|---|---|
| Jackson-Pollock 3-site | Male | 28 | 12mm, 18mm, 15mm | ~1.0639 | ~15.31% |
| Durnin-Womersley 4-site | Female | 34 | B6, T14, S12, SI10 | ~1.0300 | ~30.49% |
| Tape method | Male | 40 | Height 175cm, Neck 40cm, Waist 92cm | ~1.0440 | ~24.17% |
| BMI-based | Female | 26 | Height 165cm, Weight 62kg | ~1.0450 | ~24.02% |
Values are approximate and depend on rounding and measurement technique.
- Jackson-Pollock 3-site (density): polynomial using sum of 3 skinfolds (mm) and age.
- Durnin-Womersley 4-site (density): D = A − B × log10(sum4), where A and B depend on age and sex.
- Tape method: estimates body fat % from circumferences, then converts to density using Siri inverse.
- BMI-based (Deurenberg): estimates body fat % from BMI, age, sex, then converts to density using Siri inverse.
Conversions from density to body fat use: %BF = (495 / D) − 450 (Siri) and %BF = (457 / D) − 414.2 (Brozek).
- Select a method that matches your tools (calipers, tape, or scale).
- Choose sex, units, and enter your age.
- Fill only the inputs needed for your chosen method.
- Press Calculate to display results above the form.
- Download CSV or PDF to save your report.
- Re-measure consistently (same side, same time) for better tracking.
1) What is body density?
Body density compares mass to volume. Higher density usually means more lean tissue relative to fat. It is used to estimate body fat percentage.
2) Which method is most accurate?
Accuracy depends on measurement quality and whether the formula fits your population. Caliper methods can be strong when done correctly; tape and BMI methods are more convenient but less direct.
3) Why do Siri and Brozek give different body fat %?
They use different assumptions about fat-free mass density. Differences are usually small, but they can widen at higher or lower body fat levels.
4) Do I need weight to calculate density?
Not for skinfold density equations. Weight is optional and only used here to estimate fat mass and lean mass after body fat percentage is known.
5) Why are my results out of range?
Out-of-range results usually come from unit mistakes, inconsistent landmarks, or impossible circumference relationships (like waist smaller than neck). Re-check measurement sites and try again.
6) How often should I measure?
Weekly or biweekly works well for most people. Measure under similar conditions each time, and focus on trends rather than single readings.
7) Is this a medical tool?
No. It provides estimates for fitness tracking. For clinical assessment, diagnosis, or treatment decisions, consult a qualified healthcare professional.