A babys height can be measured using a horizontal length scale (HLS), tape measure, or an infantometer. Before measuring your babys height, remove all their clothing and accessories. Lay them flat on the surface in a supine position with their head touching the headboard, and position them so that the soles of their feet touch the footboard. Measure their length using any tools to the nearest millimeter (11). However, for accurate height and weight measurements, ensure that a professional does it to get reliable results.