The method
The US Navy circumference formulas use logarithms of tape measures in inches. Men: waist and neck against height. Women: waist, hip, and neck against height. CheckBMI and many other sites use the same published coefficients. We use them too, with the same warning: a one-inch error at the waist moves the result more than people expect.
Measure neck below the larynx, waist at the navel level used by the method you are copying (be consistent), hip at the widest point. Relax the abdomen. Do not compare a morning tape with an evening tape and call it fat loss.
How this differs from our other estimator
The BMI-based estimator only knows BMI, age, and sex. This page knows circumferences, so it can disagree — especially in people with more or less central fat than their BMI suggests. That disagreement is useful. Read both next to BMI limitations.
Worked example
A man 70 in tall, 16 in neck, 37 in waist produces a mid-range Navy estimate. Tightening the tape by an inch can drop the percentage without any fat having moved. Treat week-to-week waist in centimetres, logged the same way, as the more honest diary. See daily metrics.
Frequently asked
Does the Navy tape calculator store what I type?
No. The arithmetic runs in your browser. See the privacy page.
Is this medical advice?
No. Read the medical disclaimer. Take unusual results to a clinician.
Should children use this?
No. These tools are written for adults.
How does this sit next to BMI?
Use the BMI calculator as a size snapshot, then return here for the question this page actually answers.
What should I read after the number?
Food: meal framework. Joints: knees or back. Metrics: adult indicators.
Formulas are named on the page. They are planning maths, not clinic devices.
Using the result in a normal week
Write the figure once. Do not recalculate after every meal. Recalculate when weight has changed by several kilograms, when a clinician has changed a medicine that affects weight or heart rate, or when your job has become much more or much less physical. Daily recalculation is how a useful tool becomes noise.
Food still comes from the meal framework, the foods list, and the dinner templates in the journal. Movement still comes from walking and from the mobility articles when a joint is the limit. Metrics still come from waist, blood pressure, and sleep on the adult-indicator pages.
If the result looks extreme, assume the inputs or the equation limits before you assume your body is extreme. Heights typed in the wrong unit are the usual villains. Then talk to a person who can examine you.
Keep the same units you used last time. Measure height once against a wall and write it in the notebook you already keep for waist, morning weight, and walks. Consistency beats precision theatre.
Using the result in a normal week
Write the figure once. Do not recalculate after every meal. Recalculate when weight has changed by several kilograms, when a clinician has changed a medicine that affects weight or heart rate, or when your job has become much more or much less physical. Daily recalculation is how a useful tool becomes noise.
Food still comes from the meal framework, the foods list, and the dinner templates. Movement still comes from walking and from the mobility articles when a joint is the limit. Metrics still come from waist, blood pressure, and sleep — see adult indicators and home blood pressure.
Shortcuts that promise to replace this work are collected in why crash diets fail and teas, wraps, and shortcuts. Read those if the reason you opened a calculator was a product promise rather than a planning question.
If the result looks extreme, assume the inputs or the equation limits before you assume your body is extreme. Heights under 140 cm or weights typed in the wrong unit are the usual villains. Then talk to a person who can examine you. A second calculator tab is not that person.
Keep the same units you used last time. Mixing pounds and kilograms, or inches and centimetres, is the most common way to get a theatrical result. When in doubt, measure height once against a wall and write it in the notebook you already keep for waist, morning weight, and walks. Consistency beats precision theatre.