Tags: Light & Optics_Reflection & Refraction, Physics, Physics_Light & Optics This round concave glass mirror is designed for physics and educational uses. It is approximately 1.5" (38mm) diameter and 2mm thick. Note, thickness varies as they are not designed to be consistent in that respect. Because of their educational use design, there may be minor imperfections that do not affect physical function. 100mm Focal Length