Our custom magnets are 15 mils (381 microns) thick. With laminate and coating, the total thickness is 19 mils (482 microns).
Keep in mind, mil is not short for millimeter. Mil is a commonly used measurement for products like magnets and stickers.
For reference, our vinyl stickers without the liner are 7 +/- mils thick. (0.007 inches or 177.8 microns). When still on the paper backing, our stickers are 15.45 mils thick (0.015 inches or 392.43 microns).