Ideally, you will want the space between each pendant to be the same as the width or diameter of each fixture. For example, if you have 18 inch pendants, the space between each fixture should be 18 inches. This rule of thumb remains true, even if the pendants are hung at staggering heights. To determine the appropriate size of your kitchen island pendants, follow the steps below:

1. Measure the length and width of your table, kitchen island, counter, bar, or desk in feet.
2. Subtract 12 inches (or 1 foot) from each of these measurements to ensure there is 6 inches of clearance on all sides of the fixture.
3. Take the remaining measurements in feet and add them together.
4. This number is the approximate width allowable of each pendant.
5. To determine the allowable number of pendants over your desired surface, take the length of your table and minus 12 inches and then divide by any number under the maximum allowable width (as determined in the previous step) and divide by two.
6. This number is the approximate number of pendants that you could hang over your kitchen island, dining room table, or counter-height bar.

So I'm getting 18 inches is a good size. But my math may be off