How do i perfectly place this part on the grid without any space between them two?

How do i perfectly place this part on the grid without any space between them two?

Hi, Currently working on this placement system and i want to make the part be on top of the grid perfectly but this wont work with other sizes..

The current size it only works for is 25, 25, 25

-- Just a part of my script

local Offset = game.Workspace.Grid.Size.Y/2 
game.Workspace.Part.CFrame = CFrame.new(0, game.Workspace.Grid.Size.Y/2 + Offset - math.floor(game.Workspace.Part.Size.Y/3)+.5 , 0)