how big is the kitchen ?? I have 4" LED's in mine, but I have 6" in other rooms. My ceiling in my kitchen is a different level, and it's not very large. so it depends on what you're working with.

4 or 5" would be fine for countertop lighting w/8' ceiling.

here's a guide

To determine how far apart to space your recessed lights, divide the height of the ceiling by two. If a room has an 8 foot ceiling, you should space your recessed lights approximately 4 feet apart. If the ceiling is 10 feet, you'll want to put about 5 feet of space in between each fixture

[https://www.houzz.com/discussions/4-or-5-or-6-led-or-cfl-recessed-lights-dsvw-vd~210656[(https://www.houzz.com/discussions/4-or-5-or-6-led-or-cfl-recessed-lights-dsvw-vd~210656)

Following

I used 4” LED cans in my kitchen renovation a few years ago with 9’ ceilings. I personally like the look better than the 6” cans. I did the same in my den.