Are smart scales accurate for body fat?

Smart scales are not very accurate for measuring your exact body fat percentage. Most consumer smart scales use bioelectrical impedance analysis (BIA), which estimates body composition from how electrical current passes through your body. That estimate can change noticeably with hydration, recent exercise, meals, alcohol, and even time of day.

They’re better for tracking trends than for getting a precise number. If you use the scale under the same conditions each time, the readings can still be useful for seeing whether your body-fat estimate is generally moving up or down.

A few important caveats:

• Foot-to-foot scales mainly measure from the feet/legs and then use formulas to estimate the rest of the body.
• Hydration changes can make readings look higher or lower than they really are.
• For a more accurate body-composition assessment, methods like DEXA are generally more informative than consumer smart scales.

If you use one, the most reliable approach is to measure at the same time of day, under the same conditions—for example, in the morning after using the bathroom and before eating or exercising.