There are formulas for this but I believe you need the diameter of the pendant. Have you picked out a pendant?

It reall depends on the pendants and we need pics of the space or at least the drawings of the plan. IMO island lighting should light the island not the ceiling and all lighting in a kitchen should be LED 4000K so keep that in mind and then go looking at pendants you like and come back with pics and dimensions of the pendants.

Hi! When I was remodeling our kitchen, I had this same question and found an answer on drivenbydecor.com that worked perfectly. Essentially, it was recommended to take the length of your island in inches and divide by 4. That number is how many inches from the ends of the island to place the center of your pendants. So, for a 10 foot island (which ours is as well), we used 2 pendants (that are 18 inches wide each) and placed the center of each 30 inches from the ends of the island. I’m very happy with this placement. If you go with skinny pendants, 3 would work but I realized once ours were installed that 3 would have definitely been too many given the width of our pendants.

Im looking at the fire pendants by Tech Lighting. Shade: Height 7.3", Diameter 4.5"

The blue is $100.... ?

13" Metal and Glass Mini Pendant, Clear, Clear Blue · More Info

13" Metal and Glass Mini Pendant, Amber/Smoke · More Info

A wider pendant, and have 2 ?

W 15" / H 4.5"

Essence, 28095LED, Pendant, Chrome · More Info

6" W glass is wavy and iridescent

the blue fire pendant by Tech Lighting is what I was looking at. Unfortunately its around $500 for one! Actually, it's more than that on the Houzz site.