Body Composition Calculator
Estimate your body fat percentage, lean mass, and fat mass from a small set of body measurements. This calculator uses two established estimation methods, Relative Fat Mass (RFM) and Taylor-McClung, to provide a practical body composition baseline before planning a cut, maintenance phase, or muscle gain phase.
Body Composition
Taking a Measurement
The Relative Fat Mass (RFM) method requires measurement at your waist just above the top of your hip bones (iliac crest), keeping the tape horizontal all the way around. Stand tall with your abdomen relaxed. Take the reading at the end of a normal exhale whilst keeping the tape snug against the skin without compressing it. Don't suck in or brace.
The Relative Fat Mass (RFM) method requires measurement at your waist just above the top of your hip bones (iliac crest), keeping the tape horizontal all the way around. Stand tall with your abdomen relaxed. Take the reading at the end of a normal exhale whilst keeping the tape snug against the skin without compressing it. Don't suck in or brace.
Method Accuracy
This calculator provides an estimated body fat percentage using the selected method, with lower and upper bounds based on each method's RMSE (root mean square error) versus DEXA reference measurements. These bounds are intended to show a realistic range for the estimate, but individual results can vary and some people may fall outside this range (for example, due to body shape, fat distribution, or measurement error). All results shown are estimations only and should not be treated as a medical or diagnostic measurement.
Next Steps
Use your results in the Energy Calculator to unlock the full set of calorie and body composition metrics. Knowing your body fat percentage enables more advanced outputs, including fat-free mass (FFM)-based insights, and helps generate more personalised calorie targets for cutting, maintenance, or gaining. Once you've calculated your body composition here, head to the Energy Calculator to view all available metrics and planning insights.