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US Navy Body Fat Method

A 1980s field formula that still beats every app and scale for accuracy without equipment.

Tape-measure body fat accurate to ±3-4% vs DEXA. The best non-imaging estimate you can do at home.

The Navy needed a field test for body fat that did not require a dunk tank or an impedance scale. They regressed circumference measurements against hydrostatic-weighing data and got a logarithmic formula that works within 3-4% of DEXA gold standard. Accurate, cheap, and requires only a tape measure.

Quick answer

Tape-measure body fat accurate to ±3-4% vs DEXA. The best non-imaging estimate you can do at home.

What you are trying to do
A 1980s field formula that still beats every app and scale for accuracy without equipment.
Best next step
Structural Density · Body Fat %
Limit to remember
Treat this as a practical aid for the task, not a replacement for professional judgment.

Key points

  • ▸ Male formula: BF% = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. Measurements in inches.
  • ▸ Female formula: BF% = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450.
  • ▸ Measurement points: neck below the larynx, waist at narrowest point (men) or at navel (women), hip at widest point (women only).
  • ▸ Accuracy: ±3-4% vs DEXA for general population. Less accurate for very muscular (thick necks under-count fat) or very obese individuals.
  • ▸ Better than BMI: distinguishes muscle from fat. A 180 lb lifter and 180 lb office worker hit the same BMI and very different Navy BF%.
  • ▸ Worse than imaging: DEXA and MRI are more accurate, but cost $100-300 per scan. Tape measure is free.

Examples

  • Male, 5'10" (70"), neck 15", waist 34"
    log10(34-15) = 1.279. log10(70) = 1.845. BF% = 495/(1.0324 − 0.19077×1.279 + 0.15456×1.845) − 450 ≈ 17.4%. Fit band.
  • Female, 5'6" (66"), neck 13", waist 28", hip 38"
    log10(28+38-13) = 1.724. BF% = 495/(1.29579 − 0.35004×1.724 + 0.22100×1.819) − 450 ≈ 25.6%. Fit band for women.
  • Muscular lifter under-count
    Male, thick 17" neck from training, 32" waist. Formula output: ~12% BF. DEXA likely reads 14-15%. Muscular neck biases the estimate low.

When to use which tool

Related

Frequently asked questions

› Why not just use a bathroom impedance scale? Troubleshooting

Impedance scales are cheap but vary 3-8% day-to-day based on hydration alone. Navy tape method is more consistent. Best practice: use both, trust the trend line, not any single reading.

› How carefully do I need to measure? How-to

Tape at skin contact without compressing. 0.25" measurement error per site creates ~1% BF estimate error. Do each site twice and average.

› How should I use this guide with a Kefiw tool? How-to

Use the guide as the plan and the linked Kefiw tool as the check. Read the steps first, try the move manually, then use the tool to compare outputs, catch edge cases, and decide whether the result actually fits your task.

› What mistake do tool guides help avoid? Troubleshooting

Tool guides help avoid using a utility mechanically without understanding what you are trying to accomplish. Most word, writing, and text utilities are fast, but speed can hide context mistakes. Know whether you are solving a puzzle, cleaning copy, drafting a line, or checking a rule.

› Can a tool guide help me learn the skill? How-to

A tool guide can help you learn if you pause before accepting the output and ask why it worked. Compare your first guess with the tool result, look for the rule or pattern, and repeat that review. Passive copying solves one task; active review builds the skill.