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Archived noindex page. Kefiw's public focus is Property decision help.

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This older Kefiw page is kept for reference, marked noindex, and removed from the primary sitemap. The current Kefiw experience is focused on property decisions: cost, quotes, damage, buying, selling, owning, and packets.

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Structural Density · Body Fat %

US Navy body fat from tape-measure circumferences — ±3–4% vs DEXA.

The Navy developed this formula in the 1980s as a field substitute for underwater weighing. Logarithmic regression of neck, waist, and (for women) hip circumferences against height. Validated ±3-4% vs DEXA — better than BMI, worse than a scan.

Part of: Body Composition & Health

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Fields marked optional can be skipped; results update as you type
Structural Density · US Navy Circumference
Load-to-Chassis Ratio
0%10%20%30%40%50%
Structural Density
11.1% Fat
Classification: Athlete
Formula: US Navy circumference method · accuracy ±3-4% vs DEXA. Measure at natural waist (narrowest point) and neck (just below larynx). Women add hip (widest point).

How to use

  1. Measure neck (below larynx), waist (narrowest point), and hip (widest, women only).
  2. Pick units and gender.
  3. Read body-fat % and classification band.

Examples

70 in · neck 15 · waist 34 · male
BF ≈ 17.4% · Fit band. Strip fat by tightening waist − neck delta.

Before you act on the result

Health-related tools are educational planning aids. They can make a number or assumption visible, but they do not diagnose, treat, prescribe, or replace clinician guidance.

If the result points to risk, symptoms, medication questions, or urgent changes, use it as a note for a qualified professional rather than a final decision.

Next up

Bones set. Now track the metabolic slope.Metabolic Incline · Waist-to-Height → Density needs protein? Partition fuel accordingly.Fuel Partitioning · Macros →

Frequently asked questions

› Why waist − neck? Troubleshooting

The Navy formula models total body volume as head + neck (lean) + trunk + limbs. Waist − neck (men) and waist + hip − neck (women) proxy trunk fat.

› Is it accurate for athletes? Trust & accuracy

Less so. Muscular necks under-count fat; deep-trained cores inflate waist slightly. Accept ±5% for trained populations.

Tips & related reading

See the Body Composition & Health hub →

Tips & how-tos

Relevant links

Related tools

Metabolic Incline · Waist-to-Height

Waist-to-height ratio — better predictor of cardiometabolic risk than BMI. "Keep your waist under half your height."

Metabolic Floor · BMR / TDEE

Calculate your Basal Metabolic Rate and Total Daily Energy Expenditure using Mifflin-St Jeor. Power-consumption view with cut / maintain / bulk zones.

Fuel Partitioning · Macros

Daily protein, fat, and carb targets anchored to bodyweight and training goal. Protein-first, fat floor second, carbs fill.