These coasters are 4 to 4 1/2 inches round.  They are fired in a 2300 degree pottery kiln  with glass chips that adds to their unique look.  Adding the glass chips makes these not food safe so they are only for decorative purposes or use as a coaster or trinket dish.  Adding glass to pottery always opens up the chance there could be pieces of glass to chip off so it is definitely not recommended for any food use.  However, the effect of adding the glass over the glaze is amazing!