I’ve done DEXA and the measurements between the two were very close

Smartwatches like the Samsung Galaxy Watch 5/6, which use wrist based sensors to measure body fat, are convenient but not very reliable. They typically have an error margin of ±3–5% (e.g., reading 17.5%–23.0% for someone who is 20%) because they only measure your torso and are sensitive to your hydration levels. A 2022 study in Obesity Facts by Kim et al. found a mean error of 3.8% for Samsung's BIA compared to a DEXA scan. The U.S. Navy Method, which uses a tape measure for your neck, waist, and hips, is a cheap alternative but has a ±4–6% error margin (e.g., 16.0%–24.0%) due to inconsistencies in measuring and variations in body shape. A 2019 study in Military Medicine by Hinton et al. reported a mean error of 4.2% for this method in men.