1/1000th of a millimeter. Layer thickness of 3D printed objects are measured in Microns. Layers of 300 microns are considered thick. Layers of 200 microns are considered medium thick. Layers of 100 microns are considered fine or thin. Layers of 50 microns or less are considered very fine. The thicker the layers of a print are the faster an object will print. Conversely the thinner the layers of a print are the longer an object will take to print.