How to Measure Body Composition on Samsung Galaxy Watch 4
The Galaxy Watch 4 was the first smartwatch with body composition analysis, using bioelectrical impedance analysis (BIA) to measure body fat percentage, muscle mass, body water, BMI, and basal metabolic rate directly from your wrist.
Taking a Measurement
The measurement takes about 15 seconds and requires specific finger placement.
- Open
Samsung Healthon your watch - Scroll to and tap
Body composition - Follow the on-screen instructions to position yourself
- Place two fingers (index and middle) on the Home button
- Place two fingers (index and middle) on the Back button simultaneously
- Hold still with firm pressure until the progress bar completes
- View your results on screen
The measurement creates a circuit through your body to analyze tissue composition.
Preparing for Accurate Results
Consistent conditions are essential for meaningful trend tracking.
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Best Time: Morning before eating or drinking, after using the bathroom
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Physical State: Dry hands (moisture affects readings), relaxed body, sitting or standing still
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Avoid Measuring: Immediately after exercise, after heavy meals, when dehydrated, or after alcohol consumption
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Consistency Matters: Measure at the same time under similar conditions daily. Daily variations of 1-3% are normal—focus on weekly and monthly trends rather than individual readings.
What Gets Measured
The watch reports five body composition metrics.
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Body Fat Percentage: Total fat as a percentage of body weight. Track decreasing trends during weight loss.
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Skeletal Muscle Mass: Weight of muscle tissue in your body. Track increasing trends during strength training.
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Body Water: Percentage of body weight that is water (normal range is 50-65%).
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Basal Metabolic Rate (BMR): Calories your body burns at rest, useful for calorie planning.
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Body Mass Index (BMI): Calculated from your height and weight, not measured by sensors.
Accuracy Expectations
Body composition readings have limitations compared to professional methods.
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Margin of Error: Expect ±3-5% variation, comparable to consumer smart scales using similar BIA technology
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Best Use: Tracking changes over time rather than absolute values. Weekly and monthly trends are more meaningful than daily readings.
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Comparison: DEXA scans and hydrostatic weighing are more accurate but cost $50-150 per session. The watch provides convenient daily tracking without extra equipment.
Who Should Not Use This Feature
The bioelectrical current poses risks for some users.
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Pacemakers or Implanted Devices: Do not use—the electrical signal can interfere with medical devices
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Pregnant Women: Not tested for safety during pregnancy
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Children Under 18: Not calibrated for developing bodies
Tracking Progress
Use body composition to verify that weight loss is fat loss, not muscle loss. If muscle mass decreases while dieting, adjust your protein intake or add strength training. Weight staying the same while body fat drops and muscle increases indicates successful body recomposition.