Since the invention of the single-handled faucet in the late 1940s, manufacturers have designed sinks to accommodate them while they continued to offer sinks designed for two-handled faucets. The placement of the holes and their size can vary, depending on whether the sink is intended for the bathroom or the kitchen, but there are usually three holes, and the unused ones typically get covered by a decorative plate. There are variations to this standard configuration, however, to accommodate specialty or custom faucets.
The Standard Sink Faucet Holes
Most sink faucets require either a single hole for the spout and handle or two holes for the two handles. These come in one of two varieties: widespread -- the holes are more than 4 inches apart -- or center set -- the holes are only 4 inches apart. You usually find three holes pre-drilled into the sink deck. They can accommodate either type of faucet, so you don't have to match the sink to the faucet. This standard configuration also allows you to switch a double-handled faucet for a single-handled one without modifying the sink.
The center set faucet handle holes are spaced 4 inches from the center of the middle hole on each side of the hole. This is a standard most faucet manufacturers conform to so when you buy a typical center set faucet, it is more easily installed right into your pre-cut sink holes. On faucets with a base plate, one or more of these holes often is covered up, but this is not always the case.
The widespread faucets feature a two handles that are anywhere from 8 to 16 inches apart on the top of your sink. This wider spread is the reason for the name. In addition, these parts also are individually spaced and presented in the sink. There is no escutcheon or baseplate connecting them all. This allows more freedom in your installation because holes may be cut into your sink manually anywhere you want them.
Other Sizes and Considerations
Along with the standards there are variations. There are mini-widespread faucets, which are not spread as far apart on the sink top, and even single handle faucets that fit a three-hole design. You can cover up the two handle holes if you choose to install a single handle faucet in a sink drilled for two handle designs. In addition, you'll find that most all faucet holes are about the same diameter, which is 1.25 inches to 1.5 inches. Always pre-match your parts with the existing sink's holes to avoid problems.