If your large family or you and a partner engage in bathroom sink wars every morning, double bathroom sinks could be the solution to a peaceful environment.
Minimum space requirements
A 60-inch wide space provides minimum comfort for two 18-inch undermount sinks, which allows a foot-long stretch of countertop between sinks and 6 inches on either side. (The rule of thumb suggests 30 inches of space from the center of one sink to the center of the second sink as well as at least 12 inches of space from the center of a sink to a wall.) For more counter space, elbowroom, and below-sink storage, strive for additional width.
Upgrading from one bowl to two
As long as the center of the new second sink is 30 inches or less away from the first sink, you can save on plumbing costs by tying into the same trap and waste line. If your sinks will be further apart or if you're adding a separate vanity and sink, you'll pay to extend plumbing and install separate water and waste lines. And, of course, in order for the sinks to match, plan to buy two new sinks and faucets. You also may need to invest in a longer vanity, unless you're opting for wall-mount or pedestal sinks.