GEMs are approximately ¾ inches in diameter. Each box contains over 1,450 Square Feet (135 Square Meters) of accessible Surface Area. MarinePure GEMs are the perfect size for canister filters, hang on the back filters or nano-tank filter systems. This amount of media is good for up to 70 gallon systems. They are the perfect solution for ammonia and nitrite elimination and most users will also see better control in their Nitrates.