11cm/4.33" diameter. The lids are colorful and pretty. Jewel acrylic knob adorns each lid. Perfect for office, home or outdoors. The gem-like knob is removable. Lid made of food grade silicone, BPA free, FDA approved. Knobmade from BPA free acrylic. Durable, reusable, non-toxic. Wash by hand or dishwasher. Silicone is safe from -40 to 230 C. Microwave safe when knob is removed. Seals on all smooth rimmed cups, mugs and glasses. Keeps out dust and bugs. Prevents liquid from sloshing out of the cup when you're walking. Helps maintain temperature of beverage.