Calculating macros based on body fat percentage rather than body mass index is more precise. Everyone has different body fat distribution. Bone Density Scans called dual-energy X-ray absorptiometry, or DEXA scans, are coveted as the most accurate method of determining body composition. DEXA scans are typically available in doctor’s offices or some gyms. A variety of reasonably reliable at-home ways to calculate your body fat percentage require things like a soft measuring tape or calibers and are more effective with a friend.