Hydrostatic Weighing
Hydrostatic (underwater) weighing is the classic gold-standard method for measuring body fat by weighing a person under water.
Plain English
Patient-Friendly Explanation
Hydrostatic weighing — also called underwater weighing — measures body fat using the principle that fat floats and muscle sinks. You are weighed in air, then weighed again while fully submerged after emptying your lungs as much as possible. Because lean tissue is denser than water and fat is less dense, the difference in the two weights reveals your body density, from which body fat percentage is calculated. It is highly accurate but impractical for routine clinics, which is why most now use bioimpedance or DEXA instead.
Medical
Clinical Definition
Hydrostatic weighing is a densitometric reference method for body composition. Body density is derived from weight in air and weight underwater, with corrections for residual lung volume and water density, then converted to percent body fat using the Siri or Brozek equations (based on assumed densities of fat mass, 0.9007 g/mL, and fat-free mass, 1.100 g/mL). It correlates well with four-compartment models and served as the criterion standard before DEXA; however, it requires submersion, is operator-dependent and unsuitable for many patients, limiting it to research settings.
Key Insight
Why It Matters
The principle behind underwater weighing — that muscle is denser than fat — is why body composition tells a fuller story than weight alone. Accord Medical uses modern, comfortable methods to track the same thing.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: August 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
