Body Fat Calculator (BIA Method)
Estimate body fat percentage using Resistance and Reactance data. Supports Deurenberg and Rush equations for accurate bio-data analysis.
About
Bioelectrical Impedance Analysis (BIA) calculates body composition by measuring the opposition to an electrical current flow through body tissues. This tool allows users with raw data from smart scales or medical devices to interpret their metrics. Muscle contains high water content and conducts electricity easily, while fat acts as an insulator (high resistance). Accuracy depends on hydration status, making it crucial to measure under consistent conditions. This calculator integrates established clinical equations to provide estimates for diverse populations.
Formulas
The calculator estimates Fat-Free Mass (FFM) first, then derives Body Fat. The general form (Lukaski/Deurenberg) is:
Once FFM is known, Body Fat Percentage (BF%) is calculated:
Reference Data
| Variable | Symbol | Typical Range | Impact on Result |
|---|---|---|---|
| Resistance | R | 300 - 800 Ω | Higher R usually indicates higher fat mass (less water). |
| Reactance | Xc | 30 - 100 Ω | Reflects cell membrane integrity and capacitance. |
| Height | H | 150 - 200 cm | Squared in the formula (H2/R) as the conductive path length. |
| Hydration | Water | 50 - 65 % | Dehydration increases Resistance, falsely elevating Body Fat %. |
| Deurenberg Const | k | Varies | Adjusts for age and gender differences in bone density. |
| Rush Const | keth | Varies | Correction factor for Asian/Polynesian bone structure. |
| Impedance Index | Zidx | 30 - 70 | Calculated as Height2Resistance. |