Ceiling joists are usually installed either 16 or 24 inches on center, which means roughly 16 or 24 inches apart. Once you’ve located the first one, the others are easier to find. If you only need to know which direction the joists run, access the attic and take a look.. Use the tape measure to map the rough location of the next joist, roughly 16 or 24 inches away from the first, and tap the ceiling with your knuckles or sweep a stud finder over the area to pinpoint the joist’s location.