Body Composition Calculators

About these tools

BMI is a quick screening number but cannot tell fat from muscle. Adding a waist-to-hip ratio shows fat distribution, and the Navy tape-measure method estimates body fat directly. Lean body mass formulas and ideal-weight ranges give further reference points. No single number tells the whole story, so use two or three together and track trends over time.

Choosing the right measure

If you only have a scale and know your height, BMI and the lean body mass formulas are available instantly. With a tape measure, add waist-to-hip ratio and the Navy body fat estimate, which say more about where fat is stored and how much you carry. Ideal-weight formulas are reference points from medicine rather than personal targets.

Consistency beats precision

Every method here has error of several percentage points or kilograms. Measure the same way, at the same time of day, every few weeks, and focus on the direction of change. If several measures move together, the trend is probably real.

Privacy and safety

Every measurement you enter stays in your browser. Body composition tools are not suitable for children, during pregnancy, or for people with an eating disorder or a history of one; if numbers like these cause distress, it is fine to skip them and focus on habits instead.

The calculators in detail

BMI Calculator

Calculates Body Mass Index and the CDC adult category, with a color scale showing where you fall. The category is based on the rounded number you see, and children and teens are directed to CDC percentile tools instead.

Body Fat Calculator

Estimates body fat percentage from a few tape measurements using the U.S. Navy method developed by Hodgdon and Beckett, then places it in American Council on Exercise categories. Best used to track trends over time.

Lean Body Mass Calculator

Estimates lean mass — everything except fat — from height, weight and sex using the Boer, James and Hume formulas, and shows the body fat each implies. Handy when you have no tape measurements.

Ideal Weight Calculator

Shows a weight range from four classic formulas (Devine, Robinson, Miller and Hamwi) alongside the weights that give a healthy BMI for your height, with careful handling of heights under five feet.

Waist-to-Hip Ratio Calculator

Divides waist by hip circumference and compares the result with the World Health Organization cutoffs of 0.90 for men and 0.85 for women, showing whether fat distribution suggests increased metabolic risk.