Rockwool Starter Cubes come in packs of 45. They are 1.5'' x 1.5'' x 1.5''.

They are individually wrapped to retain moisture longer. They have a small hole punched into them to place your seed or cutting.

You can fit 72 cubes into a standard propagation tray (6 rows by 12 rows), though you should only put in about 50 to allow for air movement between them (5 rows x 10 rows).