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Body Fat & Ideal Weight Calculator

US Navy circumference method + Devine ideal weight formula, all calculations stay on your device.

How Body Fat & Ideal Weight Calculator works

Your body fat percentage gives a more nuanced picture of body composition than BMI alone, because it distinguishes fat mass from lean mass (muscle, bone and organs). This calculator uses the US Navy circumference method: measure your height, neck circumference and waist circumference (plus hip circumference for women), and the formula estimates your fat percentage without any specialist equipment beyond a tape measure.

The tool also shows your Devine ideal body weight (a 1974 pharmacology reference used in clinical drug dosing calculations), so you can see both estimated composition and a reference weight target at a glance. The circumference method typically falls within 3 to 4 percentage points of a DEXA scan or hydrostatic weighing. All measurements in centimetres; all calculations run locally in your browser.

Written by Bastien Sulyan

How to use Body Fat & Ideal Weight Calculator, step by step

  1. Select your biological sex (the formula uses different equations for men and women).
  2. Enter your height in centimetres.
  3. Measure your neck circumference at its narrowest point and enter it in centimetres.
  4. Measure your waist circumference at the navel and enter it in centimetres.
  5. For women only: measure your hip circumference at the widest point and enter it.
  6. Read your estimated body fat percentage, fat mass, lean mass and Devine ideal weight from the result panel.

Common use cases

  • Getting a body composition baseline before starting a strength training or fat loss programme to track changes over weeks.
  • Comparing your result to the American Council on Exercise body fat ranges (essential, athlete, fitness, acceptable, obese) to understand where you stand.
  • Tracking whether a diet and exercise change over 8 to 12 weeks has shifted your estimated fat percentage, using consistent measurement technique.
  • Giving a healthcare provider an approximate body fat figure when direct measurement tools are not available at an appointment.

Frequently asked questions

Does this calculator upload my measurements?

No. Every calculation runs locally in your browser using JavaScript arithmetic. Your height, neck, waist and hip measurements are never transmitted to any server. The tool works offline once the page has loaded.

What are the US Navy formulas?

For men: body fat percentage = 495 divided by (1.0324 minus 0.19077 times log10(waist minus neck) plus 0.15456 times log10(height)) minus 450. For women: body fat percentage = 495 divided by (1.29579 minus 0.35004 times log10(waist plus hip minus neck) plus 0.22100 times log10(height)) minus 450. All measurements in centimetres. This formulation was derived by the US Department of Defense from a 1988 study by Hodgdon and Beckett.

How accurate is the US Navy circumference method?

In the original validation study the method correlated well with hydrostatic weighing with a standard error of about 3 to 4 percentage points. Results can vary more for individuals with unusual body proportions or very high or low muscle mass. Measurement technique matters: take each circumference at the right anatomical point and keep the tape horizontal. Average two or three readings for consistency.

What are healthy body fat percentage ranges?

General ACE reference ranges: Essential fat (men 2 to 5 percent, women 10 to 13 percent), Athletes (men 6 to 13 percent, women 14 to 20 percent), Fitness (men 14 to 17 percent, women 21 to 24 percent), Acceptable (men 18 to 24 percent, women 25 to 31 percent), Obese (men 25 percent and above, women 32 percent and above). These are reference ranges, not clinical diagnoses.

What is the Devine ideal body weight formula?

For men: ideal weight (kg) = 50 plus 2.3 kg for each inch of height above 5 feet. For women: ideal weight (kg) = 45.5 plus 2.3 kg for each inch above 5 feet. This formula was originally developed by B.J. Devine in 1974 for calculating drug doses in clinical practice. It is a pharmacological reference value, not a prescriptive weight target, and does not account for muscle mass.

Is the body fat estimate medical advice?

No. All results are estimates for general informational purposes only and should not be used to diagnose, treat or manage any health condition. Body composition norms vary by age, ethnicity and population. Consult a healthcare professional for personalised assessment and guidance.

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