Bathroom faucets come in all shapes and sizes. Some things you need to consider when making your selections are:

the type of handles you prefer
the style you prefer
the finish you want
the requirements of the sink or lavatory it will be installed in
how much you want to spend.

The important thing you'll need to know when choosing a bathroom faucet are the design of the sink or countertop in which it will be mounted. You will need to know whether you need a single hole design, a 4 inch mini-spread or centerset, or an 8 inch widespread.
Bathroom faucets are typically set in either 4” or 8” width configurations. In the 4” set you can have a centerset or mini widespread setup; if it’s 8” or more, it is known as a widespread set. When you choose your new bathroom faucets you can change styles, but will have to stay with the same size, or replace the sink if you want to switch.

Single-Hole and Single-Lever Faucets integrate the spout and mixing handle or handles into one fitting. Compact and easy-to-use, they require only one faucet hole drilling. Some faucets will include an optional six-inch cover plate for existing four-inch drill installations.

Centerset Faucets for standard four-inch drill installations handles mounted onto a six-inch plate. These are recommended for smaller, pre-existing, pre-drilled basins.

Widespread Faucets offer the greatest design flexibility. A mini-widespread faucet has three separate pieces in a smaller, standard four-inch drilling. A widespread faucet has a standard spread or drilling of at least eight inches.

Wall-Mounted Faucets for above-the-counter and freestanding basins require a longer spout for extended reach.

Roman Tub Faucets means the fittings are mounted to the deck rather than the wall off the room or bath itself, and the spout is an arched shape.

Many bathroom faucets require additional trim to complete the faucet or faucet handle set. By allowing you to chose your own handles and trim, you have greater choices in the design and appearance of your faucet. Also, different faucet manufactures and different faucet types are purchased differently. For example, when purchasing a Moen Inspirations faucet, you must select the rough-in valve, the faucet body, the faucet accent, and the faucet accent trim pieces. Other Moen faucets might only require a handle, or come complete. Delta faucets are purchased in a similar manner. Be absolutely certain that you buy your bathroom faucet and sink at the same time and from the same source to make sure they are compatible. The sink must be drilled or have holes punched out to match the faucet you buy, and not all units will go together. Some specialty sinks require special bathroom faucets that match them. Cultured marble tops need faucets with a longer spout to fit correctly because of the setback. Never 'assume'  that everything will fit, and always ask your salesperson to verify that they will work together.

Replacing a Bathroom Sink Faucet