Three Indian documents give three depths. The DMR farmer folder says 2 to 3 cm. The 2011 manual says 3 to 4 cm. TNAU says 1 cm, pressed gently.
Do not average them. Pick one, keep it the same across every bag, and write it down, because depth is one of the few things you fully control. An uneven layer gives early pins in the thin patches and nothing in the thick ones.

