Undermount sinks mount below the countertop's surface but on top of the sink cabinet using special clips and caulking sealants. The result is a smooth, no-lip installation for a clean, modern look. Each sink is sized to work with existing countertops and faucets, so no special sizing is required. However, it is important to know a few things about the undermount sink before you select one for your kitchen.
Undermount and Faucet Sizing
The undermount sink is built to fit inside a standard 24-inch wide kitchen countertop, like a standard rimmed kitchen sink. If your undermount sink is 20 inches wide or less, it provides plenty of room to mount a faucet. The undermount sink size includes one or two bowls, which range in size from 8 to 20 inches from side to side and 18 inches from the front to the back of the sink. That leaves an inch of space in front of the sink and 3 inches behind the sink for the faucet. This is slightly different from a top-mounting, rimmed sink.
Rims and Design Considerations
The rimmed sink has a large rim around the sink bowls. This rim adds about 2 inches of overall length and width to the sink. The faucet mounting holes are inside this rim on most rimmed sinks. This means the total sink width can exceed 20 inches because no additional space behind the sink is necessary to mount the faucets. The undermount sink has no upper rim like a standard rimmed sink, just a small lip that measures less than an inch. The absence of a rim means there is more room to mount the faucet on the countertop, rather than in the sink mounting holes. Essentially, the faucet still mounts in the same position in both sinks, but in the undermount sink, it does not mount inside the sink rim.
Faucet Base Sizing
Many faucets have a base that measures between 2 and 3 inches wide. The undermount sink measures about 20 inches overall, with a rim of 1 inch. Remember, this rim is underneath the countertop, so it does not take up countertop space. If a 1-inch buffer of counter space is left in front of the sink, 3 inches more is available behind it to mount the faucet. As long as the faucet base is less than 3 inches wide and the total width of the sink is 20 inches or less, the faucet will comfortably fit on the countertop.
Before You Install
Before installing an undermount sink, it is best to double check dimensions. Measure the countertop from front to back and measure the sink from front to back. You will often find a 4-inch difference in the measurements. Trace out the dimensions for the sink installation on the countertop. Position the faucet behind it. If there is not enough room, slide the sink mounting area forward. You may mount the sink as close to the front of the counter as possible without the front lip sliding in front of the edge of the cabinet.