There is no regulation for bathroom sinks. There is no recommended shape, type or style. But the choice of a vanity sink is not arbitrary. Bathroom sinks coordinate with room decor, application, and most importantly, available countertop space.
The Basic Sink
Basic bathroom sink installation is a single cabinet, topped off with a laminate or tile countertop. Also known as a drop-in, top-mount or self-rimmed sink, it drops into a hole cut into a plywood or particle board top. Metal clips on the underneath side tighten to secure the sink to the countertop. The majority of sinks are predrilled with holes for the faucet.
Measure for a Drop-In Sink
The size of a drop-in sink is based on how much room is available on the countertop. The typical round vanity sink is 16 to 20 inches in diameter -- oval shapes may be wider -- with a basin depth of between 5 to 8 inches. Basin depth is for the most part, a matter of personal choice, because there's usually plenty of space underneath.
Measure for Depth
Measure the countertop. If it's a drawing, measure it to scale. The depth, front to back, of a standard vanity countertop is standardized at about 22 inches. The standard 16-to-20-inch sink fits into the countertop with a typical 2-inch space in front, with the space behind the faucet variable.
Measure For Width
The width of the sink is determined by how much countertop space is available on either side. If the countertop is only 22 to 24 inches wide, there's only room to center the average 16-to-20-inch sink. If you have over 24 inches of countertop width, it's fine to install an oval-shaped sink that's wider, but wise to leave 4 to 6 inches or more of countertop space on either side for bath essentials. It's fine to shift the sink to one side, if that's your preference, instead of centering it.
Measure For the Hole
Measuring for the hole is an important step. The typical drop-in, or self-rimmed sink has a 3/8-to-1/2-inch-wide lip around the perimeter. If you purchase a new sink, it may or may not come with a template. If it has a template, use it to cut the hole.
Cut the Hole Without a Template
Place the sink upside down on the countertop and trace around it if you don't have a template. Remove the sink and draw another line 3/8 inch inside the tracing. Cut the hole and test fit the sink. If it's too tight, trim off a bit more and test fit until the lip fits flat against the countertop.
If your sink doesn't fit on the first attempt, it may be that it's not shaped perfectly, or the hole is not cut perfectly. Look for scuff marks on the sink where it's binding in the hole. Remove the corresponding high spots on the cut-out with a file.
All Other Sinks
Measurements for sink styles other than top mount are based on available room in the bathroom, or the size of the cabinet.
Integrated sinks are molded composite sinks. The one-piece countertop fits on the existing vanity cabinet, with the sink molded into the surface. Measure for integrated sinks by measuring the width and length of the cabinet, and add 3/4 to 1 inch for overhang on the front. Add a 1/2-to-3/4-inch overhang to the sides if desired.
Undermount sinks install to the bottom of the countertop, which is typically stone, granite or composite. Sink holes for undermount sinks are measured and cut by the manufacturer of the countertop who gives it a finished edge. Measure the width and length of the sink, and the width and length of the countertop. Give the measurements to the manufacturer or dealer and they will take it from there.
A throw-back to an early era, the vessel sink sits on top of the countertop. Contemporary versions are all different sizes and shapes. The water passes down through the countertop via a small drain pipe. The size and shape of the sink is a matter of personal choice -- if it fits on the countertop, it works.
Pedestal and wall-mount sinks do not utilize cabinetry. The plumbing pipes are exposed underneath, however shrouds or columns can be added to hide the pipes. These sinks are small, typically no more than 22 to 24 inches. Purchase them according to how much room you want to give up for the sink. Use this type of sink when space is at a premium.