Wall studs on houses in the United States are usually located 16 inches apart. Some studs on older houses may be located 24 inches apart, though the spacing is usually never greater than this.
One easy way to locate a stud in a wall is by looking at the trim at a wall outlet. Outlets are mounted to a stud on one side, so the general location of a stud can be easily determined. From that stud location, measuring 16 inches in either direction with a tape measure should reveal the location of the other studs in the wall. The trim at the bottom of a wall may also reveal stud locations by looking at the nails in the trim, as these are usually hammered into wall studs.