What is the common size for a residential bathroom sink drain?

The common size for a residential bathroom sink drain is typically 1.25 inches. This size is standard in plumbing because it strikes a balance between adequate drainage capacity while fitting well with most sink designs and plumbing systems. A 1.25-inch drain allows for proper flow rates, reducing the risk of clogs and ensuring effective waste removal from the sink.

In contrast, a 1.5-inch drain is more commonly used for kitchen sinks or other fixtures that handle larger volumes of water and waste. A 1.00-inch drain is generally too small for a bathroom sink, leading to potential drainage issues. Lastly, a 2.00-inch drain is even larger than necessary for typical bathroom fixtures and is typically reserved for commercial applications or specialized floor drains. Hence, 1.25 inches is the most appropriate size for residential bathroom sink drains.